Organometallic Complex, Light-Emitting Element, Light-Emitting Device, Electronic Device, and Lighting Device

ABSTRACT

As a novel substance having a novel skeleton, a novel organometallic complex that can emit phosphorescence in the green to red wavelength region and has high emission efficiency and a high yield of synthesis is provided. One embodiment of the present invention is an organometallic complex in which a diketone having a five-membered or six-membered alicyclic structure composed of carbon and hydrogen is a ligand. 
     
       
         
         
             
             
         
       
     
     In the formula, L represents a bidentate aromatic ligand and has at least a bond between carbon of an aromatic ring in the aromatic ligand and Ir. X represents a five-membered or six-membered alicycle composed of carbon and hydrogen. Further, R 1  represents a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms.

BACKGROUND OF THE INVENTION

1. Field of the Invention

One embodiment of the present invention relates to an organometalliccomplex. In particular, one embodiment of the present invention relatesto an organometallic complex that is capable of converting a tripletexcited state into luminescence. In addition, one embodiment of thepresent invention relates to a light-emitting element, a light-emittingdevice, an electronic device, and a lighting device each using theorganometallic complex.

2. Description of the Related Art

Organic compounds are brought into an excited state by the absorption oflight. Through this excited state, various reactions (photochemicalreactions) are caused in some cases, or luminescence is generated insome cases. Therefore, the organic compounds have a wide range ofapplications.

As one example of the photochemical reactions, a reaction of singletoxygen with an unsaturated organic molecule (oxygen addition) is known.Since the ground state of an oxygen molecule is a triplet state, oxygenin a singlet state (singlet oxygen) is not generated by directphotoexcitation. However, in the presence of another triplet excitedmolecule, singlet oxygen is generated to cause an oxygen additionreaction. In this case, a compound capable of forming the tripletexcited molecule is referred to as a photosensitizer.

As described above, for generation of singlet oxygen, a photosensitizercapable of forming a triplet excited molecule by photoexcitation isneeded. However, the ground state of an ordinary organic compound is asinglet state; therefore, photoexcitation to a triplet excited state isforbidden transition and generation of a triplet excited molecule isdifficult. A compound that can easily cause intersystem crossing fromthe singlet excited state to the triplet excited state (or a compoundthat allows the forbidden transition of photoexcitation directly to thetriplet excited state) is thus required as such a photosensitizer. Inother words, such a compound can be used as the photosensitizer and isuseful.

The above compound often exhibits phosphorescence. Phosphorescencerefers to luminescence generated by transition between differentenergies in multiplicity. In an ordinary organic compound,phosphorescence refers to luminescence generated in returning from thetriplet excited state to the singlet ground state (in contrast,fluorescence refers to luminescence in returning from the singletexcited state to the singlet ground state). Application fields of acompound capable of exhibiting phosphorescence, that is, a compoundcapable of converting the triplet excited state into luminescence(hereinafter, referred to as a phosphorescent compound), include alight-emitting element including an organic compound as a light-emittingsubstance.

This light-emitting element has a simple structure in which alight-emitting layer including an organic compound that is alight-emitting substance is provided between electrodes. Thislight-emitting element has attracted attention as a next-generation flatpanel display element in terms of characteristics such as being thin andlight in weight, high speed response, and direct current low voltagedriving. Further, a display device including this light-emitting elementis superior in contrast, image quality, and wide viewing angle.

The light-emitting element including an organic compound as alight-emitting substance has a light emission mechanism that is of acarrier injection type: a voltage is applied between electrodes where alight-emitting layer is interposed, electrons and holes injected fromthe electrodes recombine to put the light-emitting substance into anexcited state, and then light is emitted in returning from the excitedstate to the ground state. As in the case of photoexcitation describedabove, types of the excited state include a singlet excited state (S*)and a triplet excited state (T*). The statistical generation ratiothereof in the light-emitting element is considered to be S*:T*=1:3.

At room temperature, a compound capable of converting a singlet excitedstate into luminescence (hereinafter, referred to as a fluorescentcompound) exhibits only luminescence from the singlet excited state(fluorescence), not luminescence from the triplet excited state(phosphorescence). Accordingly, the internal quantum efficiency (theratio of the number of generated photons to the number of injectedcarriers) of a light-emitting element including the fluorescent compoundis assumed to have a theoretical limit of 25%, on the basis ofS*:T*=1:3.

On the other hand, in a case of a light-emitting element including thephosphorescent compound described above, the internal quantum efficiencythereof can be improved to 75% to 100% in theory; namely, the emissionefficiency thereof can be 3 to 4 times as much as that of thelight-emitting element including a fluorescent compound. Therefore, thelight-emitting element including a phosphorescent compound has beenactively developed in recent years in order to achieve a highlyefficient light-emitting element. An organometallic complex thatcontains iridium or the like as a central metal is particularlyattracting attention as a phosphorescent compound because of its highphosphorescence quantum yield (refer to Patent Document 1, PatentDocument 2, and Patent Document 3).

REFERENCE Patent Document

-   [Patent Document 1] Japanese Published Patent Application No.    2007-137872-   [Patent Document 2] Japanese Published Patent Application No.    2008-069221-   [Patent Document 3] International Publication WO 2008/035664    Pamphlet

SUMMARY OF THE INVENTION

While blue or green phosphorescent materials have been developed asreported in Patent Documents 1 to 3, what is also important in view ofextension of the range of light-emitting materials is development ofmaterials having novel skeletons.

Thus, as a novel substance having a novel skeleton, one embodiment ofthe present invention provides a novel organometallic complex that canemit phosphorescence in the green to red wavelength region and has highemission efficiency and a high yield of synthesis. One embodiment of thepresent invention provides a light-emitting element, a light-emittingdevice, an electronic device, or a lighting device with high emissionefficiency.

One embodiment of the present invention is an organometallic complex inwhich a diketone having a five-membered or six-membered alicyclicstructure composed of carbon and hydrogen is a ligand. Therefore, oneembodiment of the present invention is an organometallic complex havinga structure represented by General Formula (G1).

In the formula, L represents a bidentate aromatic ligand and has atleast a bond between carbon of an aromatic ring in the aromatic ligandand Ir. X represents a five-membered or six-membered alicycle composedof carbon and hydrogen. Further, R¹ represents a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms.

Note that in the above structure, it is preferable that the aromaticligand be a nitrogen-containing heteroaromatic ring derivativesubstituted by an aryl group or a nitrogen-containing heterocycliccarbene derivative substituted by an aryl group, and the site ofsubstitution of the aryl group be carbon adjacent to nitrogen atom ofnitrogen-containing heteroaromatic ring or nitrogen adjacent to carbenecarbon atom.

In the above structure, the aromatic ligand is preferably a ligandrepresented by any one of General Formulae (L1) to (L3).

In General Formulae (L1) to (L3), R⁶ to R⁹ separately representhydrogen, a substituted or unsubstituted alkyl group having 1 to 4carbon atoms, or a substituted or unsubstituted phenyl group. A² to A⁶separately represent oxygen, sulfur, nitrogen, sp² hybridized nitrogenbonded to any of an alkyl group having 1 to 4 carbon atoms and a phenylgroup, sp² hybridized carbon bonded to hydrogen, or sp² hybridizedcarbon bonded to any of an alkyl group having 1 to 4 carbon atoms and aphenyl group. Further, adjacent two atoms of A² to A⁶ may be bonded toeach other to form a ring.

Another embodiment of the present invention is an organometallic complexrepresented by General Formula (G2).

In the formula, X represents a five-membered or six-membered alicyclecomposed of carbon and hydrogen. R¹ represents a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms. Further, R² and R⁴to R⁹ separately represent a substituted or unsubstituted alkyl grouphaving 1 to 4 carbon atoms, or a substituted or unsubstituted phenylgroup.

Another embodiment of the present invention is an organometallic complexrepresented by General Formula (G3).

In the formula, X represents a five-membered or six-membered alicyclecomposed of carbon and hydrogen. R¹ represents a substituted orunsubstituted allyl group having 1 to 4 carbon atoms. Further, R², R³,and R⁵ to R⁹ separately represent a substituted or unsubstituted alkylgroup having 1 to 4 carbon atoms, or a substituted or unsubstitutedphenyl group.

Another embodiment of the present invention is an organometallic complexrepresented by Structural Formula (100).

Another embodiment of the present invention is an organometallic complexrepresented by Structural Formula (101).

Another embodiment of the present invention is an organometallic complexrepresented by Structural Formula (104).

Another embodiment of the present invention is an organometallic complexrepresented by Structural Formula (113).

Further, the organometallic complex of one embodiment of the presentinvention is very effective for the following reason: the organometalliccomplex can emit phosphorescence, that is, it can provide luminescencefrom a triplet excited state and can exhibit emission, and thereforehigher efficiency is possible when the organometallic complex is appliedto a light-emitting element. Thus, the present invention also includes alight-emitting element in which the organometallic complex of oneembodiment of the present invention is used.

Other embodiments of the present invention are not only a light-emittingdevice including the light-emitting element but also an electronicdevice and a lighting device each including the light-emitting device.The light-emitting device in this specification refers to an imagedisplay device and a light source (e.g., a lighting device). Inaddition, the light-emitting device includes, in its category, all of amodule in which a light-emitting device is connected to a connector suchas a flexible printed circuit (FPC) or a tape carrier package (TCP), amodule in which a printed wiring board is provided on the tip of a TCP,and a module in which an integrated circuit (IC) is directly mounted ona light-emitting element by a chip on glass (COG) method.

As a novel substance having a novel skeleton, one embodiment of thepresent invention can provide a novel organometallic complex that canemit phosphorescence in the green to red wavelength region and has highemission efficiency and a high yield of synthesis. Further, since theorganometallic complex that is one embodiment of the present inventionhas the novel skeleton, emission color of phosphorescence to be obtainedcan also be adjusted. With the use of the novel organometallic complex,a light-emitting element, a light-emitting device, an electronic device,or a lighting device with high emission efficiency can be provided.Alternatively, it is possible to provide a light-emitting element, alight-emitting device, an electronic device, or a lighting device withlow power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a structure of a light-emitting element.

FIG. 2 illustrates a structure of a light-emitting element.

FIGS. 3A and 3B illustrate structures of light-emitting elements.

FIG. 4 illustrates a light-emitting device.

FIGS. 5A and 5B illustrate a light-emitting device.

FIGS. 6A to 6D illustrate electronic devices.

FIGS. 7A to 7C illustrate an electronic device.

FIG. 8 illustrates lighting devices.

FIG. 9 shows a ¹H-NMR chart of [Ir(mppm)₂(accam)] (abbreviation).

FIG. 10 shows an ultraviolet-visible absorption spectrum and an emissionspectrum of [Ir(mppm)₂(accam)] (abbreviation).

FIG. 11 shows a ¹H-NMR chart of [Ir(mppm)₂(achex)] (abbreviation).

FIG. 12 shows an ultraviolet-visible absorption spectrum and an emissionspectrum of [Ir(mppm)₂(achex)] (abbreviation).

FIG. 13 shows a ¹H-NMR chart of [Ir(mppm)₂(acpen)] (abbreviation).

FIG. 14 shows an ultraviolet-visible absorption spectrum and an emissionspectrum of [Ir(mppm)₂(acpen)] (abbreviation).

FIG. 15 shows a ¹H-NMR chart of [Ir(tppr)₂(achex)] (abbreviation).

FIG. 16 shows an ultraviolet-visible absorption spectrum and an emissionspectrum of [Ir(tppr)₂(achex)] (abbreviation).

FIG. 17 illustrates a light-emitting element.

FIG. 18 shows current density-luminance characteristics of alight-emitting element 1.

FIG. 19 shows voltage-luminance characteristics of a light-emittingelement 1.

FIG. 20 shows luminance-current efficiency characteristics of alight-emitting element 1.

FIG. 21 shows voltage-current characteristics of a light-emittingelement 1.

FIG. 22 shows an emission spectrum of a light-emitting element 1.

FIG. 23 shows current density-luminance characteristics of alight-emitting element 2.

FIG. 24 shows voltage-luminance characteristics of a light-emittingelement 2.

FIG. 25 shows luminance-current efficiency characteristics of alight-emitting element 2.

FIG. 26 shows voltage-current characteristics of a light-emittingelement 2.

FIG. 27 shows an emission spectrum of a light-emitting element 2.

FIG. 28 shows current density-luminance characteristics of alight-emitting element 3.

FIG. 29 shows voltage-luminance characteristics of a light-emittingelement 3.

FIG. 30 shows luminance-current efficiency characteristics of alight-emitting element 3.

FIG. 31 shows voltage-current characteristics of a light-emittingelement 3.

FIG. 32 shows an emission spectrum of a light-emitting element 3.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. Note that thepresent invention is not limited to the description below, and modes anddetails thereof can be modified in various ways without departing fromthe spirit and the scope of the present invention. Therefore, thepresent invention should not be construed as being limited to thedescription of the following embodiments.

Embodiment 1

In this embodiment, organometallic complexes which are embodiments ofthe present invention are described.

An organometallic complex that is one embodiment of the presentinvention is an organometallic complex in which a diketone having afive-membered or six-membered alicyclic structure composed of carbon andhydrogen is a ligand. Note that one mode of an organometallic complex inwhich a diketone having a five-membered or six-membered alicyclicstructure composed of carbon and hydrogen is a ligand and which isdescribed in this embodiment is an organometallic complex having thestructure represented by General Formula (G1).

In General Formula (G1), L represents a bidentate aromatic ligand andhas at least a bond between carbon of an aromatic ring in the aromaticligand and Ir. X represents a five-membered or six-membered alicyclecomposed of carbon and hydrogen. Further, R¹ represents a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms.

Note that specific examples of the alkyl group having 1 to 4 carbonatoms in R¹ include a methyl group, an ethyl group, a propyl group, anisopropyl group, a butyl group, a sec-butyl group, an isobutyl group,and a tert-butyl group.

Specific examples of L that is the bidentate aromatic ligand include anitrogen-containing heteroaromatic ring derivative substituted by anaryl group and a nitrogen-containing heterocyclic carbene derivativesubstituted by an aryl group, and it is preferable that the site ofsubstitution of the aryl group be carbon adjacent to nitrogen atom ofnitrogen-containing heteroaromatic ring or nitrogen adjacent to carbenecarbon atom.

Specifically, L that is the bidentate aromatic ligand is preferably aligand represented by any of General Formulae (L1) to (L3).

In General Formulae (L1) to (L3), R⁶ to R⁹ separately representhydrogen, a substituted or unsubstituted alkyl group having 1 to 4carbon atoms, or a substituted or unsubstituted phenyl group. A² to A⁶separately represent oxygen, sulfur, nitrogen, sp² hybridized nitrogenbonded to any of an alkyl group having 1 to 4 carbon atoms and a phenylgroup, sp² hybridized carbon bonded to hydrogen, or sp² hybridizedcarbon bonded to any of an alkyl group having 1 to 4 carbon atoms and aphenyl group. Further, adjacent two atoms of A² to A⁶ may be bonded toeach other to form a ring.

Note that in an organometallic complex that is one embodiment of thepresent invention, a diketone having a five-membered or six-memberedalicyclic structure composed of carbon and hydrogen is a ligand. Thatis, the ligand has a β-diketone structure, whereby solubility of theorganometallic complex in an organic solvent is increased andpurification is enhanced, which is preferable. The β-diketone structureis preferably included for realization of an organometallic complex withhigh emission efficiency. Inclusion of the β-diketone structure hasadvantages such as a higher sublimation property and excellentevaporativity.

One embodiment of the present invention is an organometallic complexrepresented by General Formula (G2).

In General Formula (G2), X represents a five-membered or six-memberedalicycle composed of carbon and hydrogen. R¹ represents a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms. Further, R² and R⁴to R⁹ separately represent a substituted or unsubstituted alkyl grouphaving 1 to 4 carbon atoms, or a substituted or unsubstituted phenylgroup. Note that specific examples of R¹ are the same as those of R¹ inGeneral Formula (G1). Further, specific examples of R² and R⁴ to R⁹include a phenyl group as well as the specific examples of R¹ in GeneralFormula (G1).

One embodiment of the present invention is an organometallic complexrepresented by General Formula (G3).

In General Formula (G3), X represents a five-membered or six-memberedalicycle composed of carbon and hydrogen. R¹ represents a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms. R², R³, and R⁵ toR⁹ separately represent a substituted or unsubstituted alkyl grouphaving 1 to 4 carbon atoms, or a substituted or unsubstituted phenylgroup. Note that specific examples of R¹ are the same as those of R¹ inGeneral Formula (G1). Further, specific examples of R², R³, and R⁵ to R⁹include a phenyl group as well as the specific examples of R¹ in GeneralFormula (G1).

Next, specific structural formulae of the above-described organometalliccomplexes each of which is one embodiment of the present invention willbe shown (Structural Formulae (100) to (123)). Note that the presentinvention is not limited thereto.

Note that organometallic complexes represented by Structural Formulae(100) to (123) are novel substances capable of emitting phosphorescence.Note that there can be geometrical isomers and stereoisomers of thesesubstances depending on the type of the ligand. The organometalliccomplex according to one embodiment of the present invention includesall of these isomers.

Next, an example of a method of synthesizing an organometallic complexhaving the structure represented by General Formula (G1) is described.

Method of Synthesizing β-diketone Derivative Represented by GeneralFormula (G0)

An example of a method of synthesizing a β-diketone derivativerepresented by General Formula (G0) is described.

In General Formula (G0), X represents a five-membered or six-memberedalicycle composed of carbon and hydrogen. R¹ represents a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms.

Synthesis Scheme (A) of the β-diketone derivative represented by GeneralFormula (G0) is shown below.

Note that in Synthesis Scheme (A), a cyclic ketone and a carboxylic acidderivative (e.g., carboxylic acid chloride, carboxylic acid ester,carboxylic acid anhydride, and carboxylic acid amide) are reacted toyield the β-diketone derivative (G0). Note that there are a plurality ofknown methods of synthesizing the β-diketone derivative (G0), any ofwhich can be employed.

Since the above-described cyclic ketone and carboxylic acid derivativeare commercially available or their synthesis is feasible, a greatvariety of β-diketone derivatives can be synthesized as the β-diketonederivative represented by General Formula (G0). Thus, a feature of theorganometallic complex which is one embodiment of the present inventionis the abundance of ligand variations.

Method of Synthesizing Organometallic Complex of One Embodiment of thePresent Invention Represented by General Formula (G1′)

Next, a synthesis method of an organometallic complex represented byGeneral Formula (G1′), in which the bidentate aromatic ligand (L) in theorganometallic complex (G1) is the ligand represented by General Formula(L1), will be described. The organometallic complex represented byGeneral Formula (G1′) is an example of the organometallic complex (G1)which is formed using the β-diketone derivative represented by GeneralFormula (G0) and which is one embodiment of the present invention.

In General Formula (G1′), X represents a five-membered or six-memberedalicycle composed of carbon and hydrogen. R¹ represents a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms. Further, R⁶ to R⁹separately represent hydrogen, a substituted or unsubstituted alkylgroup having 1 to 4 carbon atoms, or a substituted or unsubstitutedphenyl group. A³ to A⁶ separately represent oxygen, sulfur, nitrogen,sp² hybridized nitrogen bonded to any of an alkyl group having 1 to 4carbon atoms and a phenyl group, sp² hybridized carbon bonded tohydrogen, or sp² hybridized carbon bonded to any of an alkyl grouphaving 1 to 4 carbon atoms and a phenyl group. Further, adjacent twoatoms of A² to A⁶ may be bonded to each other to form a ring.

Shown below is Synthesis Scheme (B) of the organometallic complex whichis represented by General Formula (G1′) and in which a diketone having afive-membered or six-membered alicyclic structure composed of carbon andhydrogen is a ligand.

In Synthesis Scheme (B), Y represents a halogen, and R⁶ to R⁹ separatelyrepresent hydrogen, a substituted or unsubstituted alkyl group having 1to 4 carbon atoms, or a substituted or unsubstituted phenyl group. A³ toA⁶ separately represent oxygen, sulfur, nitrogen, sp² hybridizednitrogen bonded to any of an alkyl group having 1 to 4 carbon atoms anda phenyl group, sp² hybridized carbon bonded to hydrogen, or sp²hybridized carbon bonded to any of an alkyl group having 1 to 4 carbonatoms and a phenyl group. Further, adjacent two atoms of A³ to A⁶ may bebonded to each other to form a ring.

As shown in Synthesis Scheme (B), a bidentate aromatic ligandrepresented by General Formula (L1) and an Ir compound which contains ahalogen (e.g., iridium chloride, iridium bromide, or iridium iodide) areheated in an inert gas atmosphere by using no solvent, an alcohol-basedsolvent (e.g., glycerol, ethylene glycol, 2-methoxyethanol, or2-ethoxyethanol) alone, or a mixed solvent of water and one or more ofthe alcohol-based solvents, whereby a dinuclear complex (P), which isone type of an organometallic complex including a halogen-bridgedstructure, can be obtained.

There is no particular limitation on a heating means, and an oil bath, asand bath, or an aluminum block may be used. Alternatively, microwavescan be used as a heating means.

Further, as shown in Synthesis Scheme (C), the dinuclear complex (P)obtained in Synthesis Scheme (B) is reacted with the β-diketonederivative represented by General Formula (G0) in an inert gasatmosphere, whereby a proton of the β-diketone derivative represented byGeneral Formula (G0) is eliminated and the β-diketone derivativerepresented by General Formula (G0) coordinates to the central metal Ir.Thus, the organometallic complex that is one embodiment of the presentinvention, represented by General Formula (G1′), can be obtained.

In Synthesis Scheme (C), Y represents a halogen, R¹ represents asubstituted or unsubstituted alkyl group having 1 to 4 carbon atoms, andR⁶ to R⁹ separately represent hydrogen, a substituted or unsubstitutedalkyl group having 1 to 4 carbon atoms, or a substituted orunsubstituted phenyl group. A³ to A⁶ separately represent oxygen,sulfur, nitrogen, sp² hybridized nitrogen bonded to any of an alkylgroup having 1 to 4 carbon atoms and a phenyl group, sp² hybridizedcarbon bonded to hydrogen, or sp² hybridized carbon bonded to any of analkyl group having 1 to 4 carbon atoms and a phenyl group. Further,adjacent two atoms of A³ to A⁶ may be bonded to each other to form aring.

There is no particular limitation on a heating means, and an oil bath, asand bath, or an aluminum block may be used. Alternatively, microwavescan be used as a heating means.

Note that the β-diketone derivative (G0) having the five-membered orsix-membered alicyclic structure composed of carbon and hydrogen inGeneral Formula (G1′) has a β-diketone structure, whereby solubility ofthe organometallic complex in an organic solvent is increased andpurification is enhanced, which is preferable. The β-diketone structureis preferably included for realization of an organometallic complex withhigh emission efficiency. Inclusion of the β-diketone structure hasadvantages such as a higher sublimation property and excellentevaporativity.

The bidentate aromatic ligand is preferably a ligand represented by anyone of General Formulae (L1) to (L3). Since these ligands have highcoordinative ability, and are inexpensively available or can besynthesized easily, they are useful.

In General Formulae (L1) to (L3), R⁶ to R⁹ separately representhydrogen, a substituted or unsubstituted alkyl group having 1 to 4carbon atoms, or a substituted or unsubstituted phenyl group. A² to A⁶separately represent oxygen, sulfur, nitrogen, sp² hybridized nitrogenbonded to any of an alkyl group having 1 to 4 carbon atoms and a phenylgroup, sp² hybridized carbon bonded to hydrogen, or sp² hybridizedcarbon bonded to any of an alkyl group having 1 to 4 carbon atoms and aphenyl group. Further, adjacent two atoms of A² to A⁶ may be bonded toeach other to form a ring.

The above is the description of the example of a method of synthesizingan organometallic complex that is one embodiment of the presentinvention; however, the present invention is not limited thereto and anyother synthesis method may be employed.

The above-described organometallic complex that is one embodiment of thepresent invention can emit phosphorescence and thus can be used as alight-emitting material or a light-emitting substance of alight-emitting element.

With the use of the organometallic complex that is one embodiment of thepresent invention, a light-emitting element, a light-emitting device, anelectronic device, or a lighting device with high emission efficiencycan be obtained. Alternatively, it is possible to obtain alight-emitting element, a light-emitting device, an electronic device,or a lighting device with low power consumption.

The structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 2

In this embodiment, a light-emitting element in which the organometalliccomplex described in Embodiment 1 as one embodiment of the presentinvention is used for a light-emitting layer is described with referenceto FIG. 1.

In a light-emitting element described in this embodiment, as illustratedin FIG. 1, an EL layer 102 including a light-emitting layer 113 isprovided between a pair of electrodes (a first electrode (anode) 101 anda second electrode (cathode) 103), and the EL layer 102 includes ahole-injection layer 111, a hole-transport layer 112, anelectron-transport layer 114, an electron-injection layer 115, a chargegeneration layer (E) 116, and the like in addition to the light-emittinglayer 113.

By application of a voltage to such a light-emitting element, holesinjected from the first electrode 101 side and electrons injected fromthe second electrode 103 side recombine in the light-emitting layer 113to raise the organometallic complex to an excited state. Then, light isemitted when the organometallic complex in the excited state returns tothe ground state. Thus, the organometallic complex of one embodiment ofthe present invention functions as a light-emitting substance in thelight-emitting element.

The hole-injection layer 111 included in the EL layer 102 is a layercontaining a substance having a high hole-transport property and anacceptor substance. When electrons are extracted from the substancehaving a high hole-transport property owing to the acceptor substance,holes are generated. Thus, holes are injected from the hole-injectionlayer 111 into the light-emitting layer 113 through the hole-transportlayer 112.

The charge generation layer (E) 116 is a layer containing a substancehaving a high hole-transport property and an acceptor substance. Owingto the acceptor substance, electrons are extracted from the substancehaving a high hole-transport property and the extracted electrons areinjected from the electron-injection layer 115 having anelectron-injection property into the light-emitting layer 113 throughthe electron-transport layer 114.

A specific example in which the light-emitting element described in thisembodiment is manufactured is described.

For the first electrode (anode) 101 and the second electrode (cathode)103, a metal, an alloy, an electrically conductive compound, a mixturethereof, and the like can be used. Specifically, indium oxide-tin oxide(indium tin oxide), indium oxide-tin oxide containing silicon or siliconoxide, indium oxide-zinc oxide (indium zinc oxide), indium oxidecontaining tungsten oxide and zinc oxide, gold (Au), platinum (Pt),nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe),cobalt (Co), copper (Cu), palladium (Pd), and titanium (Ti) can be used.In addition, an element belonging to Group 1 or Group 2 of the periodictable, for example, an alkali metal such as lithium (Li) or cesium (Cs),an alkaline earth metal such as calcium (Ca) or strontium (Sr),magnesium (Mg), an alloy containing such an element (MgAg, AlLi), a rareearth metal such as europium (Eu) or ytterbium (Yb), an alloy containingsuch an element, graphene, and the like can be used. The first electrode(anode) 101 and the second electrode (cathode) 103 can be formed by, forexample, a sputtering method, an evaporation method (including a vacuumevaporation method), or the like.

As the substance having a high hole-transport property which is used forthe hole-injection layer 111, the hole-transport layer 112, and thecharge generation layer (E) 116, the following can be given, forexample: aromatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′,4″-tris(carbazol-9-yl)triphenylamine(abbreviation: TCTA), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB);3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1);3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2);3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1); and the like. In addition, the followingcarbazole derivatives and the like, can be used:4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), and9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA).The substances mentioned here are mainly ones that have a hole mobilityof 10⁻⁶ cm²/Vs or higher. Note that other than these substances, anysubstance that has a property of transporting more holes than electronsmay be used.

Further, a high molecular compound such as poly(N-vinylcarbazole)(abbreviation: PVK); poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), orpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:Poly-TPD) can be used.

As examples of the acceptor substance that is used for thehole-injection layer 111 and the charge generation layer (E) 116, atransition metal oxide or an oxide of a metal belonging to any of Group4 to Group 8 of the periodic table can be given. Specifically,molybdenum oxide is particularly preferable.

The light-emitting layer 113 contains the organometallic complexdescribed in Embodiment 1 as a guest material serving as alight-emitting substance and a substance that has higher tripletexcitation energy than this organometallic complex as a host material.

Preferable examples of the substance (i.e., host material) used fordispersing any of the above-described organometallic complexes include:any of compounds having an arylamine skeleton, such as2,3-bis(4-diphenylaminophenyl)quinoxaline (abbreviation: TPAQn) and NPB,carbazole derivatives such as CBP and4,4′,4″-tris(carbazol-9-yl)triphenylamine (abbreviation: TCTA), andmetal complexes such as bis[2-(2-hydroxyphenyl)pyridinato]zinc(abbreviation: Znpp₂), bis[2-(2-hydroxyphenyl)benzoxazolato]zinc(abbreviation: Zn(BOX)₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq), and tris(8-quinolinolato)aluminum (abbreviation: Alq₃).Alternatively, a high molecular compound such as PVK can be used.

Note that in the case where the light-emitting layer 113 contains theabove-described organometallic complex (guest material) and the hostmaterial, phosphorescence with high emission efficiency can be obtainedfrom the light-emitting layer 113.

The electron-transport layer 114 is a layer containing a substancehaving a high electron-transport property. For the electron-transportlayer 114, metal complexes such as Alg₃,tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq₂), BAlq,Zn(BOX)₂, or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation:Zn(BTZ)₂) can be used. Alternatively, a heteroaromatic compound such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: Bphen),bathocuproine (abbreviation: BCP), or4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs) can beused. Further alternatively, a high molecular compound such aspoly(2,5-pyridinediyl) (abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py), orpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy) can be used. The substances mentioned here aremainly ones that have an electron mobility of 10⁻⁶ cm²/Vs or higher.Note that other than these substances, any substance that has a propertyof transporting more electrons than holes may be used for theelectron-transport layer.

Further, the electron-transport layer 114 is not limited to a singlelayer, and a stacked layer in which two or more layers containing any ofthe above-described substances are stacked may be used.

The electron-injection layer 115 is a layer containing a substancehaving a high electron-injection property. For the electron-injectionlayer 115, an alkali metal, an alkaline earth metal, or a compoundthereof, such as lithium fluoride (LiF), cesium fluoride (CsF), calciumfluoride (CaF₂), or lithium oxide (LiOx), can be used. Alternatively, arare earth metal compound such as erbium fluoride (ErF₃) can be used.Further alternatively, the substances for forming the electron-transportlayer 114, which are described above, can be used.

Alternatively, a composite material in which an organic compound and anelectron donor (donor) are mixed may be used for the electron-injectionlayer 115. Such a composite material is excellent in anelectron-injection property and an electron-transport property becauseelectrons are generated in the organic compound by the electron donor.In this case, the organic compound is preferably a material excellent intransporting the generated electrons. Specifically, for example, thesubstances for forming the electron-transport layer 114 (e.g., a metalcomplex and a heteroaromatic compound), which are described above, canbe used. As the electron donor, a substance showing an electron-donatingproperty with respect to the organic compound may be used. Specifically,an alkali metal, an alkaline earth metal, and a rare earth metal arepreferable, and lithium, cesium, magnesium, calcium, erbium, ytterbium,and the like are given. In addition, alkali metal oxide or alkalineearth metal oxide such as lithium oxide, calcium oxide, barium oxide,and the like can be given. A Lewis base such as magnesium oxide canalternatively be used. An organic compound such as tetrathiafulvalene(abbreviation: TTF) can alternatively be used.

Note that each of the above-described hole-injection layer 111,hole-transport layer 112, light-emitting layer 113, electron-transportlayer 114, electron-injection layer 115, and charge generation layer (E)116 can be formed by a method such as an evaporation method (e.g., avacuum evaporation method), an ink-jet method, or a coating method.

In the above-described light-emitting element, current flows due to apotential difference generated between the first electrode 101 and thesecond electrode 103 and holes and electrons recombine in the EL layer102, whereby light is emitted. Then, the emitted light is extractedoutside through one or both of the first electrode 101 and the secondelectrode 103. Therefore, one or both of the first electrode 101 and thesecond electrode 103 are electrodes having a light-transmittingproperty.

The above-described light-emitting element can emit phosphorescenceoriginating from the organometallic complex and thus can have higherefficiency than a light-emitting element using a fluorescent compound.

Note that the light-emitting element described in this embodiment is anexample of a light-emitting element manufactured using theorganometallic complex that is one embodiment of the present invention.Further, as a light-emitting device including the above light-emittingelement, a passive matrix light-emitting device and an active matrixlight-emitting device can be manufactured. It is also possible tomanufacture a light-emitting device with a microcavity structureincluding a light-emitting element which is a different light-emittingelement from the above light-emitting elements as described in anotherembodiment. Each of the above light-emitting devices is included in thepresent invention.

Note that there is no particular limitation on the structure of the TFTin the case of manufacturing the active matrix light-emitting device.For example, a staggered TFT or an inverted staggered TFT can be used asappropriate. Further, a driver circuit formed over a TFT substrate maybe formed of both an n-type TFT and a p-type TFT or only either ann-type TFT or a p-type TFT. Further more, there is also no particularlimitation on crystallinity of a semiconductor film used for the TFT.For example, an amorphous semiconductor film, a crystallinesemiconductor film, or the like can be given. And also, an oxidesemiconductor film, or the like can be used as a material of asemiconductor film used for the TFT.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 3

In this embodiment, as one embodiment of the present invention, alight-emitting element in which two or more kinds of organic compoundsas well as a phosphorescent organometallic iridium complex are used fora light-emitting layer is described.

A light-emitting element described in this embodiment includes an ELlayer 203 between a pair of electrodes (an anode 201 and a cathode 202)as illustrated in FIG. 2. Note that the EL layer 203 includes at least alight-emitting layer 204 and may include a hole-injection layer, ahole-transport layer, an electron-transport layer, an electron-injectionlayer, a charge generation layer (E), and the like. Note that for thehole-injection layer, the hole-transport layer, the electron-transportlayer, the electron-injection layer, and the charge generation layer(E), the substances described in Embodiment 2 can be used.

The light-emitting layer 204 described in this embodiment contains aphosphorescent compound 205 using the phosphorescent organometalliciridium complex described in Embodiment 1, a first organic compound 206,and a second organic compound 207. Note that the phosphorescent compound205 is a guest material in the light-emitting layer 204. Moreover, oneof the first organic compound 206 and the second organic compound 207,the content of which is higher than that of the other in thelight-emitting layer 204, is a host material in the light-emitting layer204.

When the light-emitting layer 204 has the structure in which the guestmaterial is dispersed in the host material, crystallization of thelight-emitting layer can be suppressed. Further, it is possible tosuppress concentration quenching due to high concentration of the guestmaterial, and thus the light-emitting element can have higher emissionefficiency.

Note that it is preferable that a triplet excitation energy level (T₁level) of each of the first organic compound 206 and the second organiccompound 207 be higher than that of the phosphorescent compound 205. Thereason for this is that, when the T₁ level of the first organic compound206 (or the second organic compound 207) is lower than that of thephosphorescent compound 205, the triplet excitation energy of thephosphorescent compound 205, which is to contribute to light emission,is quenched by the first organic compound 206 (or the second organiccompound 207) and accordingly the emission efficiency decreases.

Here, for improvement in efficiency of energy transfer from a hostmaterial to a guest material, Förster mechanism (dipole-dipoleinteraction) and Dexter mechanism (electron exchange interaction), whichare known as mechanisms of energy transfer between molecules, areconsidered. According to the mechanisms, it is preferable that anemission spectrum of a host material (a fluorescence spectrum in energytransfer from a singlet excited state, and a phosphorescence spectrum inenergy transfer from a triplet excited state) largely overlap with anabsorption spectrum of a guest material (specifically, a spectrum in anabsorption band on the longest wavelength (lowest energy) side).However, in general, it is difficult to obtain an overlap between afluorescence spectrum of a host material and an absorption spectrum inan absorption band on the longest wavelength (lowest energy) side of aguest material. The reason for this is as follows: if the fluorescencespectrum of the host material overlaps with the absorption spectrum inthe absorption band on the longest wavelength (lowest energy) side ofthe guest material, since a phosphorescence spectrum of the hostmaterial is located on a longer wavelength (lower energy) side than thefluorescence spectrum, the T₁ level of the host material becomes lowerthan the T₁ level of the phosphorescent compound and the above-describedproblem of quenching occurs; yet, when the host material is designed insuch a manner that the T₁ level of the host material is higher than theT₁ level of the phosphorescent compound in order to avoid the problem ofquenching, the fluorescence spectrum of the host material is shifted tothe shorter wavelength (higher energy) side, and thus the fluorescencespectrum does not have any overlap with the absorption spectrum in theabsorption band on the longest wavelength (lowest energy) side of theguest material. For that reason, in general, it is difficult to obtainan overlap between a fluorescence spectrum of a host material and anabsorption spectrum in an absorption band on the longest wavelength(lowest energy) side of a guest material so as to maximize energytransfer from a singlet excited state of a host material.

Thus, in this embodiment, a combination of the first organic compoundand the second organic compound preferably forms an exciplex (alsoreferred to as excited complex). In that case, the first organiccompound 206 and the second organic compound 207 form an exciplex at thetime of recombination of carriers (electrons and holes) in thelight-emitting layer 204. Thus, in the light-emitting layer 204, afluorescence spectrum of the first organic compound 206 and that of thesecond organic compound 207 are converted into an emission spectrum ofthe exciplex which is located on a longer wavelength side. Moreover,when the first organic compound and the second organic compound areselected in such a manner that the emission spectrum of the exciplexlargely overlaps with the absorption spectrum of the guest material,energy transfer from a singlet excited state can be maximized. Note thatalso in the case of a triplet excited state, energy transfer from theexciplex, not the host material, is assumed to occur.

For the phosphorescent compound 205, the phosphorescent organometalliciridium complex described in Embodiment 1 is used. Although thecombination of the first organic compound 206 and the second organiccompound 207 can be determined such that an exciplex is formed, acombination of a compound which is likely to accept electrons (acompound having an electron-trapping property) and a compound which islikely to accept holes (a compound having a hole-trapping property) ispreferably employed.

As examples of a compound which is likely to accept electrons, thefollowing can be given:2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II),2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III),7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:7mDBTPDBq-II), and6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:6mDBTPDBq-II).

As examples of a compound which is likely to accept holes, the followingcan be given: 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBA1BP),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1),4,4′,4″-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation:1′-TNATA),2,7-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-spiro-9,9′-bifluorene(abbreviation: DPA2SF),N,N′-bis(9-phenylcarbazol-3-yl)-N,N′-diphenylbenzene-1,3-diamine(abbreviation: PCA2B),N-(9,9-dimethyl-2-N′,N′-diphenylamino-9H-fluoren-7-yl)diphenylamine(abbreviation: DPNF),N,N′,N″-triphenyl-N,N′,N″-tris(9-phenylcarbazol-3-yl)benzene-1,3,5-triamine(abbreviation: PCA3B),2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: PCASF),2-[N-(4-diphenylaminophenyl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: DPASF),N,N′-bis[4-(carbazol-9-yl)phenyl]-N,N′-diphenyl-9,9-dimethylfluorene-2,7-diamine(abbreviation: YGA2F),4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (abbreviation: TPD),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),N-(9,9-dimethyl-9H-fluoren-2-yl)-N-{9,9-dimethyl-2-[N′-phenyl-N′-(9,9-dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine(abbreviation: DFLADFL),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3-[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA1),3,6-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA2),4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD),3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole(abbreviation: PCzTPN2), and3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2).

As for the above-described first and second organic compounds 206 and207, the present invention is not limited to the above examples. Thecombination is determined so that an exciplex can be formed, theemission spectrum of the exciplex overlaps with the absorption spectrumof the phosphorescent compound 205, and the peak of the emissionspectrum of the exciplex has a longer wavelength than the peak of theabsorption spectrum of the phosphorescent compound 205.

Note that in the case where a compound which is likely to acceptelectrons and a compound which is likely to accept holes are used forthe first organic compound 206 and the second organic compound 207,carrier balance can be controlled by the mixture ratio of the compounds.Specifically, the ratio of the first organic compound to the secondorganic compound is preferably 1:9 to 9:1.

In the light-emitting element described in this embodiment, energytransfer efficiency can be improved owing to energy transfer utilizingan overlap between an emission spectrum of an exciplex and an absorptionspectrum of a phosphorescent compound; accordingly, it is possible toachieve high external quantum efficiency of the light-emitting element.

Note that in another structure of the present invention, thelight-emitting layer 204 can be formed using a host molecule having ahole-trapping property and a host molecule having an electron-trappingproperty as the two kinds of organic compounds other than thephosphorescent compound 205 (guest material) so that a phenomenon (guestcoupled with complementary hosts: GCCH) occurs in which holes andelectrons are introduced to guest molecules existing in the two kinds ofhost molecules and the guest molecules are brought into an excitedstate.

At this time, the host molecule having a hole-trapping property and thehost molecule having an electron-trapping property can be respectivelyselected from the above-described compounds which are likely to acceptholes and the above-described compounds which are likely to acceptelectrons.

Note that the light-emitting element described in this embodiment is anexample of a structure of a light-emitting element; it is possible toapply a light-emitting element having another structure, which isdescribed in another embodiment, to a light-emitting device that is oneembodiment of the present invention. Further, as a light-emitting deviceincluding the above light-emitting element, a passive matrixlight-emitting device and an active matrix light-emitting device can bemanufactured. It is also possible to manufacture a light-emitting devicewith a microcavity structure including a light-emitting element which isa different light-emitting element from the above light-emittingelements as described in another embodiment. Each of the abovelight-emitting devices is included in the present invention.

Note that there is no particular limitation on the structure of the TFTin the case of manufacturing the active matrix light-emitting device.For example, a staggered TFT or an inverted staggered TFT can be used asappropriate. Further, a driver circuit formed over a TFT substrate maybe formed of both an n-type TFT and a p-type TFT or only either ann-type TFT or a p-type TFT. Furthermore, there is also no particularlimitation on crystallinity of a semiconductor film used for the TFT.For example, an amorphous semiconductor film, a crystallinesemiconductor film, or the like can be given. And also, an oxidesemiconductor film, or the like can be used as a material of asemiconductor film used for the TFT.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 4

In this embodiment, as one embodiment of the present invention, alight-emitting element (hereinafter referred to as tandem light-emittingelement) in which a charge generation layer is provided between aplurality of EL layers is described.

A light-emitting element described in this embodiment is a tandemlight-emitting element including a plurality of EL layers (a first ELlayer 302(1) and a second EL layer 302(2)) between a pair of electrodes(a first electrode 301 and a second electrode 304) as illustrated inFIG. 3A.

In this embodiment, the first electrode 301 functions as an anode, andthe second electrode 304 functions as a cathode. Note that the firstelectrode 301 and the second electrode 304 can have structures similarto those described in Embodiment 2. In addition, although the pluralityof EL layers (the first EL layer 302(1) and the second EL layer 302(2))may have a structure similar to that of the EL layer described inEmbodiment 2 or 3, any of the EL layers may have a structure similar tothat of the EL layer described in Embodiment 2 or 3. In other words, thestructures of the first EL layer 302(1) and the second EL layer 302(2)may be the same or different from each other and can be similar to thatof the EL layer described in Embodiment 2 or 3.

Further, a charge generation layer (I) 305 is provided between theplurality of EL layers (the first EL layer 302(1) and the second ELlayer 302(2)). The charge generation layer (I) 305 has a function ofinjecting electrons into one of the EL layers and injecting holes intothe other of the EL layers when a voltage is applied between the firstelectrode 301 and the second electrode 304. In this embodiment, when avoltage is applied such that the potential of the first electrode 301 ishigher than that of the second electrode 304, the charge generationlayer (I) 305 injects electrons into the first EL layer 302(1) andinjects holes into the second EL layer 302(2).

Note that in terms of light extraction efficiency, the charge generationlayer (I) 305 preferably has a light-transmitting property with respectto visible light (specifically, the charge generation layer (I) 305 hasa visible light transmittance of 40% or more). Further, the chargegeneration layer (I) 305 functions even if it has lower conductivitythan the first electrode 301 or the second electrode 304.

The charge generation layer (I) 305 may have either a structure in whichan electron acceptor (acceptor) is added to an organic compound having ahigh hole-transport property or a structure in which an electron donor(donor) is added to an organic compound having a high electron-transportproperty. Alternatively, both of these structures may be stacked.

In the case of the structure in which an electron acceptor is added toan organic compound having a high hole-transport property, as theorganic compound having a high hole-transport property, for example, anaromatic amine compound such as NPB, TPD, TDATA, MTDATA, or4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), or the like can be used. The substances mentionedhere are mainly ones that have a hole mobility of 10⁻⁶ cm²/Vs or higher.However, other than the above-described substances, any organic compoundthat has a property of transporting more holes than electrons may beused.

Further, as the electron acceptor,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, or the like can be used. Alternatively, atransition metal oxide can be used. Further alternatively, an oxide ofmetals that belong to Group 4 to Group 8 of the periodic table can beused. Specifically, it is preferable to use vanadium oxide, niobiumoxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide,manganese oxide, or rhenium oxide because the electron-acceptingproperty is high. Among these, molybdenum oxide is especially preferablebecause it is stable in the air, has a low hygroscopic property, and iseasily handled.

On the other hand, in the case of the structure in which an electrondonor is added to an organic compound having a high electron-transportproperty, as the organic compound having a high electron-transportproperty for example, a metal complex having a quinoline skeleton or abenzoquinoline skeleton, such as Alq, Almq₃, BeBq₂, or BAlq, or the likecan be used. Alternatively, it is possible to use a metal complex havingan oxazole-based ligand or a thiazole-based ligand, such as Zn(BOX)₂ orZn(BTZ)₂. Further alternatively, instead of a metal complex, it ispossible to use PBD, OXD-7, TAZ, Bphen, BCP, or the like. The substancesmentioned here are mainly ones that have an electron mobility of 10⁻⁶cm²/Vs or higher. Note that other than the above-described substances,any organic compound that has a property of transporting more electronsthan holes may be used.

As the electron donor, it is possible to use an alkali metal, analkaline earth metal, a rare earth metal, a metal belonging to Group 2or 13 of the periodic table, or an oxide or a carbonate thereof.Specifically, it is preferable to use lithium (Li), cesium (Cs),magnesium (Mg), calcium (Ca), ytterbium (Yb), indium (In), lithiumoxide, cesium carbonate, or the like. Alternatively, an organic compoundsuch as tetrathianaphthacene may be used as the electron donor.

Note that forming the charge generation layer (I) 305 by using any ofthe above materials can suppress an increase in drive voltage caused bythe stack of the EL layers.

Although this embodiment shows the light-emitting element having two ELlayers, the present invention can be similarly applied to alight-emitting element in which n EL layers (302(1) to 302(n)) (n isthree or more) are stacked as illustrated in FIG. 3B. In the case wherea plurality of EL layers are included between a pair of electrodes as inthe light-emitting element according to this embodiment, by provision ofcharge generation layers (I) (305(1) to 305(n−1)) between the EL layers,light emission in a high luminance region can be obtained with currentdensity kept low. Since the current density can be kept low, the elementcan have a long lifetime. Further, in application to lighting devices, avoltage drop due to resistance of an electrode material can be reducedand accordingly homogeneous light emission in a large area is possible.Moreover, it is possible to achieve a light-emitting device of low powerconsumption, which can be driven at a low voltage.

By making the EL layers emit light of different colors from each other,the light-emitting element can provide light emission of a desired coloras a whole. For example, by forming a light-emitting element having twoEL layers such that the emission color of the first EL layer and theemission color of the second EL layer are complementary colors, thelight-emitting element can provide white light emission as a whole. Notethat the word “complementary” means color relationship in which anachromatic color is obtained when colors are mixed. In other words, whenlight obtained from a light-emitting substance and light of acomplementary color are mixed, white emission can be obtained.

Further, the same can be applied to a light-emitting element havingthree EL layers. For example, the light-emitting element as a whole canprovide white light emission when the emission color of the first ELlayer is red, the emission color of the second EL layer is green, andthe emission color of the third EL layer is blue.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 5

In this embodiment, a light-emitting device which is one embodiment ofthe present invention is described.

A light-emitting device described in this embodiment has a micro opticalresonator (microcavity) structure in which a light resonant effectbetween a pair of electrodes is utilized. The light-emitting deviceincludes, a plurality of light-emitting elements each of which has atleast an EL layer 405 between a pair of electrodes (a reflectiveelectrode 401 and a semi-transmissive and semi-reflective electrode 402)as illustrated in FIG. 4. Further, the EL layer 405 includes at least alight-emitting layer 404 serving as a light-emitting region and mayfurther include a hole-injection layer, a hole-transport layer, anelectron-transport layer, an electron-injection layer, a chargegeneration layer (E), and the like. Note that the light-emitting layer404 contains the phosphorescent organometallic iridium complex that isone embodiment of the present invention.

In this embodiment, a light-emitting device is described which includeslight-emitting elements (a first light-emitting element (R) 410R, asecond light-emitting element (G) 410G, and a third light-emittingelement (B) 410B) having different structures as illustrated in FIG. 4.

The first light-emitting element (R) 410R has a structure in which afirst transparent conductive layer 403 a; an EL layer 405 including afirst light-emitting layer (B) 404B, a second light-emitting layer (G)404G, and a third light-emitting layer (R) 404R in part; and asemi-transmissive and semi-reflective electrode 402 are sequentiallystacked over a reflective electrode 401. The second light-emittingelement (G) 410G has a structure in which a second transparentconductive layer 403 b, the EL layer 405, and the semi-transmissive andsemi-reflective electrode 402 are sequentially stacked over thereflective electrode 401. The third light-emitting element (B) 410B hasa structure in which the EL layer 405 and the semi-transmissive andsemi-reflective electrode 402 are sequentially stacked over thereflective electrode 401.

Note that the reflective electrode 401, the EL layer 405, and thesemi-transmissive and semi-reflective electrode 402 are common to thelight-emitting elements (the first light-emitting element (R) 410R, thesecond light-emitting element (G) 410G, and the third light-emittingelement (B) 410B). The first light-emitting layer (B) 404B emits light(λ_(B)) having a peak in a wavelength region from 420 nm to 480 nm. Thesecond light-emitting layer (G) 404G emits light (λ_(G)) having a peakin a wavelength region from 500 nm to 550 nm. The third light-emittinglayer (R) 404R emits light (λ_(R)) having a peak in a wavelength regionfrom 600 nm to 760 nm. Thus, in each of the light-emitting elements (thefirst light-emitting element (R) 410R, the second light-emitting element(G) 410G, and the third light-emitting element (B) 410B), light emittedfrom the first light-emitting layer (B) 404B, light emitted from thesecond light-emitting layer (G) 404G, and light emitted from the thirdlight-emitting layer (R) 404R overlap with each other; accordingly,light having a broad emission spectrum that covers a visible lightregion can be emitted. Note that the above wavelengths satisfy therelation of λ_(B)<λ_(G)<λ_(R).

Each of the light-emitting elements described in this embodiment has astructure in which the EL layer 405 is interposed between the reflectiveelectrode 401 and the semi-transmissive and semi-reflective electrode402. Light, emitted in all directions from the light-emitting layersincluded in the EL layer 405 is resonated by the reflective electrode401 and the semi-transmissive and semi-reflective electrode 402 whichfunction as a micro optical resonator (microcavity). Note that thereflective electrode 401 is formed using a conductive material havingreflectivity, and a film whose visible light reflectivity is 40% to100%, preferably 70% to 100%, and whose resistivity is 1×10⁻² Ωcm orlower is used. In addition, the semi-transmissive and semi-reflectiveelectrode 402 is formed using a conductive material having reflectivityand a conductive material having a light-transmitting property, and afilm whose visible light reflectivity is 20% to 80%, preferably 40% to70%, and whose resistivity is 1×10⁻² Ωcm or lower is used.

In this embodiment, the thicknesses of the transparent conductive layers(the first transparent conductive layer 403 a and the second transparentconductive layer 403 b) provided in the first light-emitting element (R)410R and the second light-emitting element (G) 410G, respectively, arevaried between the light-emitting elements, whereby the light-emittingelements differ in the optical path length from the reflective electrode401 to the semi-transmissive and semi-reflective electrode 402. In otherwords, in light having a broad emission spectrum, which is emitted fromthe light-emitting layers of each of the light-emitting elements, lightwith a wavelength that is resonated between the reflective electrode 401and the semi-transmissive and semi-reflective electrode 402 can beenhanced while light with a wavelength that is not resonatedtherebetween can be attenuated. Thus, when the elements differ in theoptical path length from the reflective electrode 401 to thesemi-transmissive and semi-reflective electrode 402, light withdifferent wavelengths can be extracted.

Note that the optical path length (also referred to as optical distance)is expressed as a product of an actual distance and a refractive index,and in this embodiment, is a product of an actual thickness and n(refractive index). That is, an optical path length=actual thickness×n.

Further, the total thickness from the reflective electrode 401 to thesemi-transmissive and semi-reflective electrode 402 is set to mλ_(R)/2(m is a natural number) in the first light-emitting element (R) 410R;the total thickness from the reflective electrode 401 to thesemi-transmissive and semi-reflective electrode 402 is set to mλ_(G)/2(m is a natural number) in the second light-emitting element (G) 410G;and the total thickness from the reflective electrode 401 to thesemi-transmissive and semi-reflective electrode 402 is set to mλ_(B)/2(m is a natural number) in the third light-emitting element (B) 410B.

In this manner, the light (λ_(R)) emitted from the third light-emittinglayer (R) 404R included in the EL layer 405 is mainly extracted from thefirst light-emitting element (R) 410R, the light (λ_(G)) emitted fromthe second light-emitting layer (G) 404G included in the EL layer 405 ismainly extracted from the second light-emitting element (G) 410G, andthe light (λ_(B)) emitted from the first light-emitting layer (B) 404Bincluded in the EL layer 405 is mainly extracted from the thirdlight-emitting element (B) 410B. Note that the light extracted from eachof the light-emitting elements is emitted from the semi-transmissive andsemi-reflective electrode 402 side.

Further, strictly speaking, the total thickness from the reflectiveelectrode 401 to the semi-transmissive and semi-reflective electrode 402can be the total thickness from a reflection region in the reflectiveelectrode 401 to a reflection region in the semi-transmissive andsemi-reflective electrode 402. However, it is difficult to preciselydetermine the positions of the reflection regions in the reflectiveelectrode 401 and the semi-transmissive and semi-reflective electrode402; therefore, it is assumed that the above effect can be sufficientlyobtained wherever the reflection regions may be set in the reflectiveelectrode 401 and the semi-transmissive and semi-reflective electrode402.

Next, in the first light-emitting element (R) 410R, the optical pathlength from the reflective electrode 401 to the third light-emittinglayer (R) 404R is adjusted to a desired thickness ((2 m′+1)λ_(R)/4,where m′ is a natural number); thus, light emitted from the thirdlight-emitting layer (R) 404R can be amplified. Light (first reflectedlight) that is reflected by the reflective electrode 401 of the lightemitted from the third light-emitting layer (R) 404R interferes withlight (first incident light) that directly enters the semi-transmissiveand semi-reflective electrode 402 from the third light-emitting layer(R) 404R. Therefore, by adjusting the optical path length from thereflective electrode 401 to the third light-emitting layer (R) 404R tothe desired value ((2 m′+1)λ_(R)/4, where m′ is a natural number), thephases of the first reflected light and the first incident light can bealigned with each other and the light emitted from the thirdlight-emitting layer (R) 404R can be amplified.

Note that strictly speaking, the optical path length from the reflectiveelectrode 401 to the third light-emitting layer (R) 404R can be theoptical path length from a reflection region in the reflective electrode401 to a light-emitting region in the third light-emit/ting layer (R)404R. However, it is difficult to precisely determine the positions ofthe reflection region in the reflective electrode 401 and thelight-emitting region in the third light-emitting layer (R) 404R;therefore, it is assumed that the above effect can be sufficientlyobtained wherever the reflection region and the light-emitting regionmay be set in the reflective electrode 401 and the third light-emittinglayer (R) 404R, respectively.

Next, in the second light-emitting element (G) 410G, the optical pathlength from the reflective electrode 401 to the second light-emittinglayer (G) 404G is adjusted to a desired thickness ((2 m″+1)λ_(G)/4,where m″ is a natural number); thus, light emitted from the secondlight-emitting layer (G) 404G can be amplified. Light (second reflectedlight) that is reflected by the reflective electrode 401 of the lightemitted from the second light-emitting layer (G) 404G interferes withlight (second incident light) that directly enters the semi-transmissiveand semi-reflective electrode 402 from the second light-emitting layer(G) 404G. Therefore, by adjusting the optical path length from thereflective electrode 401 to the second light-emitting layer (G) 404G tothe desired value ((2 m″+1)λ_(G)/4, where m″ is a natural number), thephases of the second reflected light and the second incident light canbe aligned with each other and the light emitted from the secondlight-emitting layer (G) 404G can be amplified.

Note that strictly speaking, the optical path length from the reflectiveelectrode 401 to the second light-emitting layer (G) 404G can be theoptical path length from a reflection region in the reflective electrode401 to a light-emitting region in the second light-emitting layer (G)404G. However, it is difficult to precisely determine the positions ofthe reflection region in the reflective electrode 401 and thelight-emitting region in the second light-emitting layer (G) 404G;therefore, it is assumed that the above effect can be sufficientlyobtained wherever the reflection region and the light-emitting regionmay be set in the reflective electrode 401 and the second light-emittinglayer (G) 404G, respectively.

Next, in the third light-emitting element (B) 410B, the optical pathlength from the reflective electrode 401 to the first light-emittinglayer (B) 404B is adjusted to a desired thickness ((2 m′″+1)λ_(B)/4,where m′″ is a natural number); thus, light emitted from the firstlight-emitting layer (B) 404B can be amplified. Light (third reflectedlight) that is reflected by the reflective electrode 401 of the lightemitted from the first light-emitting layer (B) 404B interferes withlight (third incident light) that directly enters the semi-transmissiveand semi-reflective electrode 402 from the first light-emitting layer(B) 404B. Therefore, by adjusting the optical path length from thereflective electrode 401 to the first light-emitting layer (B) 404B tothe desired value ((2 m′″+1)λ_(B)/4, where m′″ is a natural number), thephases of the third reflected light and the third incident light can bealigned with each other and the light emitted from the firstlight-emitting layer (B) 404B can be amplified.

Note that strictly speaking, the optical path length from the reflectiveelectrode 401 to the first light-emitting layer (B) 404B in the thirdlight-emitting element can be the optical path length from a reflectionregion in the reflective electrode 401 to a light-emitting region in thefirst light-emitting layer (B) 404B. However, it is difficult toprecisely determine the positions of the reflection region in thereflective electrode 401 and the light-emitting region in the firstlight-emitting layer (B) 404B; therefore, it is assumed that the aboveeffect can be sufficiently obtained wherever the reflection region andthe light-emitting region may be set in the reflective electrode 401 andthe first light-emitting layer (B) 404B, respectively.

Note that although each of the light-emitting elements in theabove-described structure includes a plurality of light-emitting layersin the EL layer, the present invention is not limited thereto; forexample, the structure of the tandem light-emitting element which isdescribed in Embodiment 4 can be combined, in which case a plurality ofEL layers and a charge generation layer interposed therebetween areprovided in one light-emitting element and one or more light-emittinglayers are formed in each of the EL layers.

The light-emitting device described in this embodiment has a microcavitystructure, in which light with wavelengths which differ depending on thelight-emitting elements can be extracted even when they include the sameEL layers, so that it is not needed to form light-emitting elements forthe colors of R, G, and B. Therefore, the above structure isadvantageous for full color display owing to easiness in achievinghigher resolution display or the like. In addition, emission intensitywith a predetermined wavelength in the emission direction can beincreased, whereby power consumption can be reduced. The above structureis particularly useful in the case of being applied to a color display(image display device) including pixels of three or more colors but mayalso be applied to lighting or the like.

Embodiment 6

In this embodiment, a light-emitting device including a light-emittingelement in which the organometallic complex that is one embodiment ofthe present invention is used for a light-emitting layer is described.

The light-emitting device can be either a passive matrix light-emittingdevice or an active matrix light-emitting device. Note that any of thelight-emitting elements described in the other embodiments can beapplied to the light-emitting device described in this embodiment.

In this embodiment, an active matrix light-emitting device is describedwith reference to FIGS. 5A and 5B.

Note that FIG. 5A is a top view illustrating a light-emitting device andFIG. 5B is a cross-sectional view taken along the chain line A-A′ inFIG. 5A. The active matrix light-emitting device according to thisembodiment includes a pixel portion 502 provided over an elementsubstrate 501, a driver circuit portion (a source line driver circuit)503, and a driver circuit portion (a gate line driver circuit) 504. Thepixel portion 502, the driver circuit portion 503, and the drivercircuit portion 504 are sealed between the element substrate 501 and thesealing substrate 506 with a sealant 505.

In addition, a lead wiring 507 is provided over the element substrate501. The lead wiring 507 is provided for connecting an external inputterminal through which a signal (e.g., a video signal, a clock signal, astart signal, and a reset signal) or a potential from the outside istransmitted to the driver circuit portion 503 and the driver circuitportion 504. Here is shown an example in which a flexible printedcircuit (FPC) 508 is provided as the external input terminal. Althoughthe FPC 508 is illustrated alone, this FPC may be provided with aprinted wiring board (PWB). The light-emitting device in the presentspecification includes, in its category, not only the light-emittingdevice itself but also the light-emitting device provided with the FPCor the PWB.

Next, a cross-sectional structure is described with reference to FIG.5B. The driver circuit portion and the pixel portion are formed over theelement substrate 501; here are illustrated the driver circuit portion503 which is the source line driver circuit and the pixel portion 502.

The driver circuit portion 503 is an example where a CMOS circuit isformed, which is a combination of an n-channel TFT 509 and a p-channelTFT 510. Note that a circuit included in the driver circuit portion maybe formed using various CMOS circuits, PMOS circuits, or NMOS circuits.Although this embodiment shows a driver integrated type in which thedriver circuit is formed over the substrate, the driver circuit is notnecessarily formed over the substrate, and may be formed outside thesubstrate.

The pixel portion 502 is formed of a plurality of pixels each of whichincludes a switching TFT 511, a current control TFT 512, and a firstelectrode (anode) 513 which is electrically connected to a wiring (asource electrode or a drain electrode) of the current control TFT 512.Note that an insulator 514 is formed to cover end portions of the firstelectrode (anode) 513. In this embodiment, the insulator 514 is formedusing a positive photosensitive acrylic resin.

The insulator 514 preferably has a curved surface with curvature at anupper end portion or a lower end portion thereof in order to obtainfavorable coverage by a film which is to be stacked over the insulator514. For example, in the case of using a positive photosensitive acrylicresin as a material for the insulator 514, the insulator 514 preferablyhas a curved surface with a curvature radius (0.2 μm to 3 μm) at theupper end portion. Note that the insulator 514 can be formed usingeither a negative photosensitive resin or a positive photosensitiveresin. It is possible to use, without limitation to an organic compound,either an organic compound or an inorganic compound such as siliconoxide or silicon oxynitride.

An EL layer 515 and a second electrode (cathode) 516 are stacked overthe first electrode (anode) 513. In the EL layer 515, at least alight-emitting layer is provided which contains the organometalliccomplex that is one embodiment of the present invention. Further, in theEL layer 515, a hole-injection layer, a hole-transport layer, anelectron-transport layer, an electron-injection layer, a chargegeneration layer, and the like can be provided as appropriate inaddition to the light-emitting layer.

A light-emitting element 517 is formed of a stacked structure of thefirst electrode (anode) 513, the EL layer 515, and the second electrode(cathode) 516. For the first electrode (anode) 513, the EL layer 515,and the second electrode (cathode) 516, the materials described inEmbodiment 2 can be used. Although not illustrated, the second electrode(cathode) 516 is electrically connected to an FPC 508 which is anexternal input terminal.

Although the cross-sectional view of FIG. 5B illustrates only onelight-emitting element 517, a plurality of light-emitting elements arearranged in matrix in the pixel portion 502. Light-emitting elementswhich provide three kinds of light emission (R, G, and B) areselectively formed in the pixel portion 502, whereby a light-emittingdevice capable of full color display can be fabricated. Alternatively, alight-emitting device which is capable of full color display may befabricated by a combination with color filters.

Further, the sealing substrate 506 is attached to the element substrate501 with the sealant 505, whereby a light-emitting element 517 isprovided in a space 518 surrounded by the element substrate 501, thesealing substrate 506, and the sealant 505. The space 518 may be filledwith an inert gas (such as nitrogen or argon), or the sealant 505.

An epoxy-based resin is preferably used for the sealant 505. It ispreferable that such a material do not transmit moisture or oxygen asmuch as possible. As the sealing substrate 506, a glass substrate, aquartz substrate, or a plastic substrate formed of fiberglass reinforcedplastic (FRP), poly(vinyl fluoride) (PVF), polyester, acrylic, or thelike can be used.

As described above, an active matrix light-emitting device can beobtained.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 7

In this embodiment, examples of a variety of electronic devices whichare completed using a light-emitting device are described with referenceto FIGS. 6A to 6D and FIGS. 7A to 7C. To the light-emitting device, theorganometallic complex that is one embodiment of the present inventionis applied.

Examples of the electronic devices to which the light-emitting device isapplied are a television device (also referred to as television ortelevision receiver), a monitor of a computer or the like, a camera suchas a digital camera or a digital video camera, a digital photo frame, amobile phone (also referred to as cellular phone or cellular phonedevice), a portable game machine, a portable information terminal, anaudio reproducing device, and a large-sized game machine such as apachinko machine. Specific examples of these electronic devices areillustrated in FIGS. 6A to 6D.

FIG. 6A illustrates an example of a television set. In a television set7100, a display portion 7103 is incorporated in a housing 7101. Imagescan be displayed on the display portion 7103, and the light-emittingdevice can be used for the display portion 7103. In addition, here, thehousing 7101 is supported by a stand 7105.

Operation of the television set 7100 can be performed with an operationswitch of the housing 7101 or a separate remote controller 7110. Withoperation keys 7109 of the remote controller 7110, channels and volumecan be controlled and images displayed on the display portion 7103 canbe controlled. Furthermore, the remote controller 7110 may be providedwith a display portion 7107 for displaying data output from the remotecontroller 7110.

Note that the television set 7100 is provided with a receiver, a modem,and the like. With the receiver, a general television broadcast can bereceived. Furthermore, when the television set 7100 is connected to acommunication network by wired or wireless connection via the modem,one-way (from a transmitter to a receiver) or two-way (between atransmitter and a receiver, between receivers, or the like) datacommunication can be performed.

FIG. 6B illustrates a computer having a main body 7201, a housing 7202,a display portion 7203, a keyboard 7204, an external connection port7205, a pointing device 7206, and the like. Note that this computer ismanufactured using the light-emitting device for the display portion7203.

FIG. 6C illustrates a portable game machine having two housings, ahousing 7301 and a housing 7302, which are connected with a jointportion 7303 so that the portable game machine can be opened or folded.A display portion 7304 is incorporated in the housing 7301, and adisplay portion 7305 is incorporated in the housing 7302. In addition,the portable game machine illustrated in FIG. 6C includes a speakerportion 7306, a recording medium insertion portion 7307, an LED lamp7308, input means (an operation key 7309, a connection terminal 7310, asensor 7311 (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), and a microphone 7312), and thelike. Needless to say, the structure of the portable game machine is notlimited to the above as long as the light-emitting device is used for atleast one of the display portion 7304 and the display portion 7305, andmay include other accessories as appropriate. The portable game machineillustrated in FIG. 6C has a function of reading out a program or datastored in a storage medium to display it on the display portion, and afunction of sharing information with another portable game machine bywireless communication. The portable game machine illustrated in FIG. 6Ccan have a variety of functions without limitation to the above.

FIG. 6D illustrates an example of a mobile phone. A mobile phone 7400 isprovided with a display portion 7402 incorporated in a housing 7401,operation buttons 7403, an external connection port 7404, a speaker7405, a microphone 7406, and the like. Note that the mobile phone 7400is manufactured using the light-emitting device for the display portion7402.

When the display portion 7402 of the mobile phone 7400 illustrated inFIG. 6D is touched with a finger or the like, data can be input to themobile phone 7400. Further, operations such as making a call andcomposing an e-mail can be performed by touching the display portion7402 with a finger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying images. The secondmode is an input mode mainly for inputting data such as text. The thirdmode is a display-and-input mode in which two modes of the display modeand the input mode are combined.

For example, in the case of making a call or composing an e-mail, a textinput mode mainly for inputting text is selected for the display portion7402 so that text displayed on the screen can be input. In this case, itis preferable to display a keyboard or number buttons on almost theentire screen of the display portion 7402.

When a detection device including a sensor for detecting inclination,such as a gyroscope or an acceleration sensor, is provided inside themobile phone 7400, display on the screen of the display portion 7402 canbe automatically switched by determining the orientation of the mobilephone 7400 (whether the mobile phone is placed horizontally orvertically for a landscape mode or a portrait mode).

The screen modes are switched by touching the display portion 7402 oroperating the operation buttons 7403 of the housing 7401. The screenmodes can also be switched depending on the kind of image displayed onthe display portion 7402. For example, when a signal of an imagedisplayed on the display portion is a signal of moving image data, thescreen mode is switched to the display mode. When the signal is a signalof text data, the screen mode is switched to the input mode.

Moreover, in the input mode, when input by touching the display portion7402 is not performed for a certain period while a signal detected by anoptical sensor in the display portion 7402 is detected, the screen modemay be controlled so as to be switched from the input mode to thedisplay mode.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken when thedisplay portion 7402 is touched with the palm or the finger, wherebypersonal authentication can be performed. Further, by providing abacklight or a sensing light source which emits near-infrared light inthe display portion, an image of a finger vein, a palm vein, or the likecan be taken.

FIGS. 7A and 7B illustrate a foldable tablet terminal. The tabletterminal is opened in FIG. 7A. The tablet terminal includes housings9630, a display portion 9631 a, a display portion 9631 b, a display modeswitch 9034, a power switch 9035, a power saver switch 9036, a clasp9033, and an operation switch 9038. The tablet terminal is manufacturedusing the light-emitting device for either the display portion 9631 a orthe display portion 9631 b or both.

Part of the display portion 9631 a can be a touch panel region 9632 aand data can be input when a displayed operation key 9637 is touched.Although a structure in which a half region in the display portion 9631a has only a display function and the other half region also has a touchpanel function is shown as an example, the display portion 9631 a is notlimited to the structure. The whole region in the display portion 9631 amay have a touch panel function. For example, the display portion 9631 acan display keyboard buttons in the whole region to be a touch panel,and the display portion 9631 b can be used as a display screen.

As in the display portion 9631 a, part of the display portion 9631 b canbe a touch panel region 9632 b. When a keyboard display switching button9639 displayed on the touch panel is touched with a finger, a stylus, orthe like, a keyboard can be displayed on the display portion 9631 b.

Touch input can be performed in the touch panel region 9632 a and thetouch panel region 9632 b at the same time.

The display mode switch 9034 can switch the display between portraitmode, landscape mode, and the like, and between monochrome display andcolor display, for example. The power saver switch. 9036 can controldisplay luminance in accordance with the amount of external light in useof the tablet terminal detected by an optical sensor incorporated in thetablet terminal. In addition to the optical sensor, another detectiondevice including a sensor for detecting inclination, such as a gyroscopeor an acceleration sensor, may be incorporated in the tablet terminal.

Note that FIG. 7A shows an example in which the display portion 9631 aand the display portion 9631 b have the same display area; however,without limitation thereon, one of the display portions may be differentfrom the other display portion in size and display quality. For example,higher definition images may be displayed on one of the display portions9631 a and 9631 b.

The tablet terminal is closed in FIG. 7B. The tablet terminal includesthe housings 9630, a solar cell 9633, a charge and discharge controlcircuit 9634, a battery 9635, and a DCDC converter 9636. In FIG. 7B, astructure including the battery 9635 and the DCDC converter 9636 isillustrated as an example of the charge and discharge control circuit9634.

Since the tablet terminal is foldable, the housings 9630 can be closedwhen the tablet terminal is not used. As a result, the display portion9631 a and the display portion 9631 b can be protected; thus, a tabletterminal which has excellent durability and excellent reliability interms of long-term use can be provided.

In addition, the tablet terminal illustrated in FIGS. 7A and 7B can havea function of displaying a variety of kinds of data (e.g., a stillimage, a moving image, and a text image), a function of displaying acalendar, a date, the time, or the like on the display portion, atouch-input function of operating or editing the data displayed on thedisplay portion by touch input, a function of controlling processing bya variety of kinds of software (programs), and the like.

The solar cell 9633 provided on a surface of the tablet terminal cansupply power to the touch panel, the display portion, a video signalprocessing portion, or the like. Note that the solar cell 9633 cancharge the battery 9635 supplying power to one or both of the housings9630, which is preferable. The use of a lithium ion battery as thebattery 9635 is advantageous in downsizing or the like.

The structure and the operation of the charge and discharge controlcircuit 9634 illustrated in FIG. 7B will be described with reference toa block diagram in FIG. 7C. The solar cell 9633, the battery 9635, theDCDC converter 9636, a converter 9638, switches SW1 to SW3, and thedisplay portion 9631 are illustrated in FIG. 7C, and the battery 9635,the DCDC converter 9636, the converter 9638, and the switches SW1 to SW3correspond to the charge and discharge control circuit 9634 illustratedin FIG. 7B.

First, an example of the operation in the case where power is generatedby the solar cell 9633 using external light is described. The voltage ofpower generated by the solar cell is stepped up or down by the DCDCconverter 9636 so that the power has a voltage for charging the battery9635. Then, when the power from the solar cell 9633 is used for theoperation of the display portion 9631, the switch SW1 is turned on andthe voltage of the power is stepped up or down by the converter 9638 soas to be a voltage needed for the display portion 9631. In addition,when display on the display portion 9631 is not performed, the switchSW1 is turned off and the switch SW2 is turned on so that the battery9635 may be charged.

Note that the solar cell 9633 is described as an example of a powergeneration means; however, without limitation thereon, the battery 9635may be charged using another power generation means such as apiezoelectric element or a thermoelectric conversion element (Peltierelement). For example, the battery 9635 may be charged with anon-contact power transmission module which is capable of charging bytransmitting and receiving power by wireless (without contact), oranother charge means used in combination.

It is needless to say that one embodiment of the present invention isnot limited to the electronic device illustrated in FIGS. 7A to 7C aslong as the display portion described in this embodiment is included.

As described above, the electronic devices can be obtained byapplication of the light-emitting device that is one embodiment of thepresent invention. The light-emitting device has a remarkably wideapplication range, and can be applied to electronic devices in a varietyof fields.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 8

In this embodiment, examples of a lighting device to which alight-emitting device including the organometallic complex that is oneembodiment of the present invention is applied are described withreference to FIG. 8.

FIG. 8 illustrates an example in which the light-emitting device is usedas an indoor lighting device 8001. Since the light-emitting device canhave a large area, it can be used for a lighting device having a largearea. In addition, a lighting device 8002 in which a light-emittingregion has a curved surface can also be obtained with the use of ahousing with a curved surface. A light-emitting element included in thelight-emitting device described in this embodiment is in a thin filmform, which allows the housing to be designed more freely. Therefore,the lighting device can be elaborately designed in a variety of ways.Further, a wall of the room may be provided with a large-sized lightingdevice 8003.

Moreover, when the light-emitting device is used for a table by beingused as a surface of a table, a lighting device 8004 which has afunction as a table can be obtained. When the light-emitting device isused as part of other furniture, a lighting device which has a functionas the furniture can be obtained.

In this manner, a variety of lighting devices to which thelight-emitting device is applied can be obtained. Note that suchlighting devices are also embodiments of the present invention.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Example 1 Synthesis Example 1

In this example, a synthesis method of[3-(acetyl-κO)-1,7,7-trimethyl-bicyclo[2.2.1]heptan-2-onato-κO]bis[2-(3-methyl-4-pyrimidinyl-κN3)phenyl-κC]iridium(III)(abbreviation: [Ir(mppm)₂(accam)]), the organometallic complex which isone embodiment of the present invention represented by StructuralFormula (100) in Embodiment 1, is described. The structure of[Ir(mppm)₂(accam)] is shown below.

Step 1: Synthesis of 3-Acetylcamphor (abbreviation: Haccam)

Into a flask equipped with a reflux pipe was put 1.58 g of sodiumhydride, and the air in the flask was replaced with nitrogen. Then, 40mL of dimethoxyethane (DME) and 5.00 g of (1R)-(+)-camphor were addedand this solution was heated and refluxed for 4 hours to cause areaction. The reacted solution was cooled down to room temperature. Witha dropping funnel, 12.4 g of acetyl chloride dissolved in 20 mL of DMEwas added dropwise in 15 minutes. After that, the solution was heatedand refluxed for 3 and a half hours to cause a reaction. The reactedsolution was cooled down to room temperature and 10 mL of ethanol wasadded. This solution was poured into ice water and an organic layer wasextracted with ethyl acetate. The obtained organic layer was washed witha 5% sodium carbonate aqueous solution, saturated brine, and water inthis order.

This organic layer, 30 mL of a 1 mol/L potassium hydroxide aqueoussolution, and 30 mL of methanol were put into a flask, the air in theflask was replaced with nitrogen, and the solution was stirred for 3hours. The reacted solution was separated into an organic layer and anaqueous layer. The pH of the aqueous layer was adjusted to 2 to 3 byaddition of dilute hydrochloric acid. Extraction with ethyl acetate wasperformed and the solution of the extract was combined with theseparated organic layer, washed with water, and dried with magnesiumsulfate. The solution after the drying was filtered, and the obtainedsolution was concentrated and dried. The obtained residue was purifiedby flash column chromatography (silica gel) using a mixed solvent ofhexane and ethyl acetate in a volume ratio of 10:1 as a developingsolvent, so that a β-diketone derivative Haccam, the objectivesubstance, was obtained (a pale yellow solution, 12% in yield). Thesynthesis scheme of Step 1 is shown by (a-1).

Step 2: Synthesis of3-(Acetyl-κO)-1,7,7-trimethyl-bicyclo[2.2.1]heptan-2-onato-κO]bis[2-(3-methyl-4-pyrimidinyl-κN3)phenyl-κC]iridium(III)(abbreviation: [Ir(mppm)₂(accam)])

Further, 25 mL of 2-ethoxyethanol, 1.09 g ofdi-μ-chloro-tetrakis[2-(3-methyl-4-pyrimidinyl-κN3)phenyl-κC]diiridium(III)(abbreviation: [Ir(mppm)₂Cl]₂), 0.56 g of Haccam obtained in Step 1, and1.02 g of sodium carbonate were put into a recovery flask equipped witha reflux pipe, and the reacted solution was bubbled with argon.

Then, irradiation with microwaves (2.45 GHz, 100 W) for 30 minutes wasperformed to cause a reaction. Dichloromethane was added to the reactedsolution and filtration was performed. The solvent of the filtrate wasdistilled off, and then the obtained residue was purified by flashcolumn chromatography (silica gel) using a mixed solvent of ethylacetate and dichloromethane in a volume ratio of 1:20 as a developingsolvent, to give [Ir(mppm)₂(accam)], the organometallic complexaccording to one embodiment of the present invention, as an orangepowder (36% in yield). The synthesis scheme of Step 2 is shown by (a-2).

An analysis result by nuclear magnetic resonance (¹H-NMR) spectroscopyof the orange powder obtained in Step 2 above is described below. FIG. 9shows the ¹H-NMR chart. These results revealed that [Ir(mppm)₂(accam)](abbreviation), the organometallic complex which is one embodiment ofthe present invention represented by Structural Formula (100), wasobtained in Synthesis Example 1.

¹H-NMR. δ (CDCl₃): 0.52-0.86 (m, 9H), 1.28 (m, 2H), 1.51 (m, 1H), 1.38(d, 3H), 1.95 (m, 1H), 2.50 (q, 1H), 2.78 (d, 3H), 2.81 (s, 3H), 6.36(m, 1H), 6.43 (m, 1H), 6.77 (m, 2H), 6.85 (m, 2H), 7.62 (m, 4H), 8.82(d, 1H), 8.99 (d, 1H).

Next, an ultraviolet-visible absorption spectrum (hereinafter, simplyreferred to as an “absorption spectrum”) of a dichloromethane solutionof [Ir(mppm)₂(accam)] (abbreviation) and an emission spectrum thereofwere measured. The measurement of the absorption spectrum was conductedat room temperature, for which an ultraviolet-visible lightspectrophotometer (V550 type manufactured by Japan SpectroscopyCorporation) was used and the dichloromethane solution (0.115 mmol/L)was put in a quartz cell. In addition, the measurement of the emissionspectrum was conducted at room temperature, for which a fluorescencespectrophotometer (FS920 manufactured by Hamamatsu Photonics K. K.) wasused and the degassed dichloromethane solution (0.115 mmol/L) was put ina quartz cell. Measurement results of the obtained absorption andemission spectra are shown in FIG. 10, in which the horizontal axisrepresents wavelength and the vertical axes represent absorptionintensity and emission intensity. In FIG. 10 where there are two solidlines, the thin line represents the absorption spectrum and the thickline represents the emission spectrum. Note that the absorption spectrumin FIG. 10 is the results obtained in such a way that the absorptionspectrum measured by putting only dichloromethane in a quartz cell wassubtracted from the absorption spectrum measured by putting thedichloromethane solution (0.115 mmol/L) in a quartz cell.

As shown in FIG. 10, [Ir(mppm)₂(accam)] (abbreviation), theorganometallic complex that is one embodiment of the present invention,has an emission peak at 553 nm, and yellow green light emission wasobserved from the dichloromethane solution.

Next, the absolute quantum yield of [Ir(mppm)₂(accam)] (abbreviation)which is represented by Structural Formula (100) and was obtained inthis example was measured. The measurement of the absolute quantum yieldwas conducted using an absolute quantum yield measurement systemC9920-02, manufactured by Hamamatsu Photonics K. K. The form of a samplewas a toluene solution (1×10⁻⁵ mol/L). The measurement results showedthat the quantum yield of [Ir(mppm)₂(accam)] (abbreviation), theorganometallic complex that is one embodiment of the present invention,is 79%. On the other hand, the absolute quantum yield of a compoundrepresented by Structural Formula (R01), which was subjected to themeasurement under similar conditions as a comparative example, was 77%.The above results revealed that emission efficiency is higher with theβ-diketone having a cyclic structure than with a structure not having acyclic structure, such as acetylacetone.

Example 2 Synthesis Example 2

In this example, a synthesis method of[2-(acetyl-κO)-cyclohexanonato-κO]bis[2-(3-methyl-4-pyrimidinyl-κN3)phenyl-κC]iridium(III)(abbreviation: [Ir(mppm)₂(achex)]), the organometallic complex which isone embodiment of the present invention represented by StructuralFormula (101) in Embodiment 1, is described. The structure of[Ir(mppm)₂(achex)] is shown below.

Synthesis of[2-(Acetyl-κO)-cyclohexanonato-κO]bis[2-(3-methyl-4-pyrimidinyl-κN3)phenyl-κC]iridium(III)(abbreviation: [Ir(mppm)₂(achex)])

First, 25 mL of 2-ethoxyethanol, 0.93 g ofdi-μ-chloro-tetrakis[2-(3-methyl-4-pyrimidinyl-κN3)phenyl-κC]diiridium(III)(abbreviation: [Ir(mppm)₂Cl]₂), 0.35 g of 2-acetylcyclohexanone(abbreviation: Hachex), and 0.87 g of sodium carbonate were put into arecovery flask equipped with a reflux pipe, and the reacted solution wasbubbled with argon. Then, irradiation with microwaves (2.45 GHz, 100 W)for 30 minutes was performed to cause a reaction. The reacted solutionwas filtered and the residue was washed with methanol, water, ethanol,and methanol in this order. The obtained residue was purified by flashcolumn chromatography (silica gel) using a mixed solvent of ethylacetate and dichloromethane in a volume ratio of 1:9 as a developingsolvent, to give [Ir(mppm)₂(achex)], the organometallic complexaccording to one embodiment of the present invention, as an orangepowder (11% in yield). The synthesis scheme is shown by (b-1).

An analysis result by nuclear magnetic resonance (¹H-NMR) spectroscopyof the orange powder obtained by the above synthesis method is describedbelow. FIG. 11 shows the ¹H-NMR chart. These results revealed that[Ir(mppm)₂(achex)] (abbreviation), the organometallic complex which isone embodiment of the present invention represented by StructuralFormula (101), was obtained in Synthesis Example 2.

¹H-NMR. δ (CDCl₃): 1.55 (m, 4H), 1.84 (s, 3H), 1.97 (m, 1H), 2.05 (m,1H), 2.35 (m, 2H), 2.81 (s, 6H), 6.36 (t, 2H), 6.75 (ddt, 2H), 6.84(ddt, 2H), 7.62 (m, 4H), 8.99 (d, 2H).

Next, an ultraviolet-visible absorption spectrum (hereinafter, simplyreferred to as an “absorption spectrum”) of a dichloromethane solutionof [Ir(mppm)₂(achex)] (abbreviation) and an emission spectrum thereofwere measured. The measurement of the absorption spectrum was conductedat room temperature, for which an ultraviolet-visible lightspectrophotometer (V550 type manufactured by Japan. SpectroscopyCorporation) was used and the dichloromethane solution (0.114 mmol/L)was put in a quartz cell. In addition, the measurement of the emissionspectrum was conducted at room temperature, for which a fluorescencespectrophotometer (FS920 manufactured by Hamamatsu Photonics K. K.) wasused and the degassed dichloromethane solution (0.114 mmol/L) was put ina quartz cell. Measurement results of the obtained absorption andemission spectra are shown in FIG. 12, in which the horizontal axisrepresents wavelength and the vertical axes represent absorptionintensity and emission intensity. In FIG. 12 where there are two solidlines, the thin line represents the absorption spectrum and the thickline represents the emission spectrum. Note that the absorption spectrumin FIG. 12 is the results obtained in such a way that the absorptionspectrum measured by putting only dichloromethane in a quartz cell wassubtracted from the absorption spectrum measured by putting thedichloromethane solution (0.114 mmol/L) in a quartz cell.

As shown in FIG. 12, [Ir(mppm)₂(achex)] (abbreviation), theorganometallic complex that is one embodiment of the present invention,has an emission peak at 560 nm, and yellow green light emission wasobserved from the dichloromethane solution.

Next, the absolute quantum yield of [Ir(mppm)₂(achex)] (abbreviation)which is represented by Structural Formula (101) and was obtained inthis example was measured. The measurement of the absolute quantum yieldwas conducted using an absolute quantum yield measurement systemC9920-02, manufactured by Hamamatsu Photonics K. K. The form of a samplewas a toluene solution (1×10⁻⁵ mol/L). The measurement results showedthat the quantum yield of [Ir(mppm)₂(achex)] (abbreviation), theorganometallic complex which is one embodiment of the present invention,is 83%. The above results revealed that emission efficiency is higherwith the β-diketone having a cyclic structure than with a structure nothaving a cyclic structure, such as acetylacetone.

Example 3 Synthesis Example 3

In this example, a synthesis method of[2-(acetyl-κO)-cyclopentanonato-κO]bis[2-(6-methyl-4-pyrimidinyl-κN3)phenyl-κC]iridium(III)(abbreviation: [Ir(mppm)₂(acpen)]), the organometallic complex which isone embodiment of the present invention represented by StructuralFormula (104) in Embodiment 1, is described. The structure of[Ir(mppm)₂(acpen)] is shown below.

Step 2: Synthesis of[2-(Acetyl-κO)-cyclopentanonato-κO]bis[2-(6-methyl-4-pyrimidinyl-κN3)phenyl-κC]iridium(III)(abbreviation: [Ir(mppm)₂(acpen)])

First, 25 mL of 2-ethoxyethanol, 0.95 g ofdi-β-chloro-tetrakis[2-(3-methyl-4-pyrimidinyl-κN3)phenyl-κC]diiridium(III)(abbreviation: [Ir(mppm)₂Cl]₂), 0.32 g of 2-acetylcyclopentanone(abbreviation: Hacpen), and 0.89 g of sodium carbonate were put into arecovery flask equipped with a reflux pipe, and the reacted solution wasbubbled with argon. Then, irradiation with microwaves (2.45 GHz, 100 W)for 30 minutes was performed to cause a reaction. The reacted solutionwas filtered and the residue was washed with methanol, water, andmethanol in this order. The obtained residue was purified by flashcolumn chromatography (silica gel) using a mixed solvent of ethylacetate and dichloromethane in a volume ratio of 1:9 as a developingsolvent, to give [Ir(mppm)₂(acpen)] (abbreviation), the organometalliccomplex according to one embodiment of the present invention, as anorange powder (23% in yield). The synthesis scheme is shown by (c-1).

An analysis result by nuclear magnetic resonance (¹H-NMR) spectroscopyof the orange powder obtained by the above synthesis method is describedbelow. FIG. 13 shows the ¹H-NMR chart. These results revealed that[Ir(mppm)₂(acpen)] (abbreviation), the organometallic complex which isone embodiment of the present invention represented by StructuralFormula (104), was obtained in Synthesis Example 3.

¹H-NMR. δ (CDCl₃): 1.73 (m, 2H), 1.82 (s, 3H), 2.15 (m, 2H), 2.64 (t,2H), 2.81 (s, 6H), 6.34 (d, 2H), 6.75-6.88 (m, 4H), 7.61 (m, 4H), 8.97(d, 2H).

Next, an ultraviolet-visible absorption spectrum (hereinafter, simplyreferred to as an “absorption spectrum”) of a dichloromethane solutionof [Ir(mppm)₂(acpen)] (abbreviation) and an emission spectrum thereofwere measured. The measurement of the absorption spectrum was conductedat room temperature, for which an ultraviolet-visible lightspectrophotometer (V550 type manufactured by Japan SpectroscopyCorporation) was used and the dichloromethane solution (0.132 mmol/L)was put in a quartz cell. In addition, the measurement of the emissionspectrum was conducted at room temperature, for which a fluorescencespectrophotometer (FS920 manufactured by Hamamatsu Photonics K. K.) wasused and the degassed dichloromethane solution (0.132 mmol/L) was put ina quartz cell. Measurement results of the obtained absorption andemission spectra are shown in FIG. 14, in which the horizontal axisrepresents wavelength and the vertical axes represent absorptionintensity and emission intensity. In FIG. 14 where there are two solidlines, the thin line represents the absorption spectrum and the thickline represents the emission spectrum. Note that the absorption spectrumin FIG. 14 is the results obtained in such a way that the absorptionspectrum measured by putting only dichloromethane in a quartz cell wassubtracted from the absorption spectrum measured by putting thedichloromethane solution (0.132 mmol/L) in a quartz cell.

As shown in FIG. 14, [Ir(mppm)₂(acpen)] (abbreviation), theorganometallic complex that is one embodiment of the present invention,has an emission peak at 552 nm, and yellow green light emission wasobserved from the dichloromethane solution.

Next, the absolute quantum yield of [Ir(mppm)₂(acpen)] (abbreviation)which is represented by Structural Formula (104) and was obtained inthis example was measured. The measurement of the absolute quantum yieldwas conducted using an absolute quantum yield measurement systemC9920-02, manufactured by Hamamatsu Photonics K. K. The form of a samplewas a toluene solution (1×10⁻⁵ mol/L). The measurement results showedthat the quantum yield of [Ir(mppm)₂(acpen)] (abbreviation), theorganometallic complex which is one embodiment of the present invention,is 89%. The above results revealed that emission efficiency is higherwith the β-diketone having a cyclic structure than with a structure nothaving a cyclic structure, such as acetylacetone.

Example 4 Synthesis Example 4

In this example, a synthesis method of[2-(acetyl-κO)-cyclohexanonato-κO]bis[2-(3,5-diphenyl-2-pyrazinyl-κN)phenyl-κC]iridium(III)(abbreviation: [Ir(tppr)₂(achex)]), the organometallic complex which isone embodiment of the present invention represented by StructuralFormula (113) in Embodiment 1, is described. The structure of[Ir(tppr)₂(achex)] is shown below.

Synthesis of[2-(Acetyl-κO)-cyclohexanonato-κO]bis[2-(3,5-diphenyl-2-pyrazinyl-κN)phenyl-κC]iridium(III)(abbreviation: [Ir(tppr)₂(achex)])

First, 25 mL of 2-ethoxyethanol, 0.42 g ofdi-μ-chloro-tetrakis[2-(3,5-diphenyl-2-pyrazinyl-κN)phenyl-κC]diiridium(III)(abbreviation: [Ir(tppr)₂Cl]₂), 0.27 g of 2-acetylcyclohexanone(abbreviation: Hachex), and 0.26 g of sodium carbonate were put into arecovery flask equipped with a reflux pipe, and the reacted solution wasbubbled with argon. Then, irradiation with microwaves (2.45 GHz, 100 W)for 30 minutes was performed to cause a reaction. The reacted solutionwas concentrated and dried. The obtained residue was washed with ethanoland hexane in this order, and was purified by flash columnchromatography (silica gel) using a mixed solvent of hexane anddichloromethane in a volume ratio of 1:4 as a developing solvent, togive [Ir(tppr)₂(achex)], the organometallic complex according to oneembodiment of the present invention, as a red powder (16% in yield). Thesynthesis scheme is shown by (d-1).

An analysis result by nuclear magnetic resonance (¹H-NMR) spectroscopyof the red powder obtained by the above synthesis method is describedbelow. FIG. 15 shows the ¹H-NMR chart. These results revealed that[Ir(tppr)₂(achex)] (abbreviation), the organometallic complex which isone embodiment of the present invention represented by StructuralFormula (113), was obtained in Synthesis Example 4.

¹H-NMR. δ (CDCl₃): 1.61 (m, 4H), 1.99 (s, 3H), 2.14 (m, 1H), 2.21 (m,1H), 2.43 (m, 2H), 6.48 (m, 4H), 6.64 (m, 2H), 6.90 (d, 2H), 7.55 (m,12H), 7.81 (m, 4H), 8.08 (m, 4H), 9.03 (d, 2H).

Next, an ultraviolet-visible absorption spectrum (hereinafter, simplyreferred to as an “absorption spectrum”) of a dichloromethane solutionof [Ir(tppr)₂(achex)] (abbreviation) and an emission spectrum thereofwere measured. The measurement of the absorption spectrum was conductedat room temperature, for which an ultraviolet-visible lightspectrophotometer (V550 type manufactured by Japan SpectroscopyCorporation) was used and the dichloromethane solution (0.0824 mmol/L)was put in a quartz cell. In addition, the measurement of the emissionspectrum was conducted at room temperature, for which a fluorescencespectrophotometer (FS920 manufactured by Hamamatsu Photonics K. K.) wasused and the degassed dichloromethane solution (0.0824 mmol/L) was putin a quartz cell. Measurement results of the obtained absorption andemission spectra are shown in FIG. 16, in which the horizontal axisrepresents wavelength and the vertical axes represent absorptionintensity and emission intensity. In FIG. 16 where there are two solidlines, the thin line represents the absorption spectrum and the thickline represents the emission spectrum. Note that the absorption spectrumin FIG. 16 is the results obtained in such a way that the absorptionspectrum measured by putting only dichloromethane in a quartz cell wassubtracted from the absorption spectrum measured by putting thedichloromethane solution (0.0824 mmol/L) in a quartz cell.

As shown in FIG. 16, [Ir(tppr)₂(achex)] (abbreviation), theorganometallic complex that is one embodiment of the present invention,has an emission peak at 625 nm, and red light emission was observed fromthe dichloromethane solution.

Example 5

In this example, a light-emitting element 1 in which [Ir(mppm)₂(accam)](abbreviation), the phosphorescent organometallic iridium complexrepresented by Structural Formula (100), is used for a light-emittinglayer is described with reference to FIG. 17. Chemical formulae ofmaterials used in this example are shown below.

Fabrication of Light-Emitting Element 1

First, indium tin oxide containing silicon oxide (ITSO) was depositedover a glass substrate 1100 by a sputtering method, so that a firstelectrode 1101 which functions as an anode was formed. The thickness was110 nm and the electrode area was 2 mm×2 mm.

Then, as pretreatment for forming the light-emitting element over thesubstrate 1100, UV ozone treatment was performed for 370 seconds afterwashing of a surface of the substrate with water and baking that wasperformed at 200° C. for 1 hour.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and was subjected to vacuum baking at 170° C. for 30 minutes in aheating chamber of the vacuum evaporation apparatus, and then thesubstrate 1100 was cooled down for about 30 minutes.

Next, the substrate 1100 was fixed to a holder provided in the vacuumevaporation apparatus so that a surface of the substrate 1100 over whichthe first electrode 1101 was formed faced downward. In this example, acase will be described in which a hole-injection layer 1111, ahole-transport layer 1112, a light-emitting layer 1113, anelectron-transport layer 1114, and an electron-injection layer 1115which are included in an EL layer 1102 are sequentially formed by avacuum evaporation method.

After reducing the pressure of the vacuum evaporation apparatus to 10⁻⁴Pa, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) andmolybdenum(VI) oxide were co-evaporated with a mass ratio of DBT3P-II(abbreviation) to molybdenum oxide being 4:2, whereby the hole-injectionlayer 1111 was formed over the first electrode 1101. The thickness ofthe hole-injection layer 1111 was 40 nm. Note that the co-evaporation isan evaporation method in which some different substances are evaporatedfrom some different evaporation sources at the same time.

Then, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:BPAFLP) was deposited by evaporation to a thickness of 20 nm, so thatthe hole-transport layer 1112 was formed.

Next, the light-emitting layer 1113 was formed over the hole-transportlayer 1112 in the following manner. Co-evaporated were2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II), 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBA1BP), and[3-(acetyl-κO)-1,7,7-trimethyl-bicyclo[2.2.1]heptan-2-onato-κO]bis[2-(3-methyl-4-pyrimidinyl-κN3)phenyl-κC]iridium(III)(abbreviation: [Ir(mppm)₂(accam)]) with a mass ratio of 2mDBTPDBq-II(abbreviation) to PCBA1BP (abbreviation) and [Ir(mppm)₂(accam)](abbreviation) being 0.8:0.2:0.025. The thickness of the light-emittinglayer 1113 was 40 nm.

Then, over the light-emitting layer 1113, 2mDBTPDBq-II (abbreviation)was deposited by evaporation to a thickness of 10 nm and thenbathophenanthroline (abbreviation: Bphen) was deposited by evaporationto a thickness of 20 nm, whereby the electron-transport layer 1114having a stacked structure was formed. Furthermore, lithium fluoride wasdeposited by evaporation to a thickness of 1 nm over theelectron-transport layer 1114, whereby the electron-injection layer 1115was formed.

Finally, aluminum was deposited by evaporation to a thickness of 200 nmover the electron-injection layer 1115 to form a second electrode 1103serving as a cathode; thus, the light-emitting element 1 was obtained.Note that in all the above evaporation steps, evaporation was performedby a resistance-heating method.

An element structure of the light-emitting element 1 obtained asdescribed above is shown in Table 1.

TABLE 1 Hole- Light- Electron- First Hole-injection transport emittingElectron- injection Second Electrode Layer Layer Layer transport LayerLayer Electrode Light- ITSO DBT3P-II:MoOx BPAFLP * ** Bphen LiF Alemitting (110 nm) (4:2 40 nm) (20 nm) (20 nm) (1 nm) (200 nm) Element1 * 2mDBTPDBq-II:PCBA1BP:[Ir(mppm)₂(accam)] (0.8:0.2:0.025 40 nm) **2mDBTPDBq-II (10nm)

Further, the fabricated light-emitting element 1 was sealed in a glovebox containing a nitrogen atmosphere so as not to be exposed to the air.

Operation Characteristics of Light-Emitting Element 1

Operation characteristics of the fabricated light-emitting element 1were measured. Note that the measurement was carried out at roomtemperature (under an atmosphere in which the temperature was kept at25° C.).

FIG. 18 shows current density-luminance characteristics of thelight-emitting element 1. In FIG. 18, the vertical axis representsluminance (cd/m²) and the horizontal axis represents current density(mA/cm²). FIG. 19 shows voltage-luminance characteristics of thelight-emitting element 1. In FIG. 19, the vertical axis representsluminance (cd/m²) and the horizontal axis represents voltage (V).Further, FIG. 20 shows luminance-current efficiency characteristics ofthe light-emitting element 1. In FIG. 20, the vertical axis representscurrent efficiency (cd/A) and the horizontal axis represents luminance(cd/m²). FIG. 21 shows voltage-current characteristics of thelight-emitting element 1. In FIG. 21, the vertical axis representscurrent (mA) and the horizontal axis represents voltage (V).

FIG. 20 reveals high efficiency of the light-emitting element 1 in whichpart of the light-emitting layer uses [Ir(mppm)₂(accam)] (abbreviation),the phosphorescent organometallic iridium complex that is one embodimentof the present invention. Table 2 shows initial values of maincharacteristics of the light-emitting element at a luminance of about1000 cd/m².

TABLE 2 Current Current Power Quantum Voltage Current DensityChromaticity Luminance Efficiency Efficiency Efficiency (V) (mA)(mA/cm²) (x, y) (cd/m²) (cd/A) (lm/W) (%) Light- 2.8 0.05 1.3 (0.43,0.56) 1100 86.6 97.1 23.2 emitting Element 1

The above results show that the light-emitting element 1 fabricated inthis example is a high-luminance light-emitting element having highcurrent efficiency. Moreover, as for color purity, it can be found thatthe light-emitting element exhibits yellow green light emission withexcellent color purity.

FIG. 22 shows an emission spectrum when a current at a current densityof 2.5 mA/cm² was supplied to the light-emitting element 1. As shown inFIG. 22, the emission spectrum of the light-emitting element 1 has apeak at around 550 nm and it is indicated that the peak is derived fromemission of the phosphorescent organometallic iridium complex[Ir(mppm)₂(accam)] (abbreviation).

Example 6

In this example, a light-emitting element 2 in which [Ir(mppm)₂(achex)](abbreviation), the phosphorescent organometallic iridium complexrepresented by Structural Formula (101), is used for a light-emittinglayer is described. Note that in the description of the light-emittingelement 2 in this example, FIG. 17 which is used in the description ofthe light-emitting element 1 in Example 5 is to be referred to. Chemicalformulae of materials used in this example are shown below.

Fabrication of Light-Emitting Element 2

First, indium tin oxide containing silicon oxide (ITSO) was depositedover the glass substrate 1100 by a sputtering method, so that the firstelectrode 1101 which functions as an anode was formed. The thickness was110 nm and the electrode area was 2 mm×2 mm.

Then, as pretreatment for forming the light-emitting element over thesubstrate 1100, UV ozone treatment was performed for 370 seconds afterwashing of a surface of the substrate with water and baking that wasperformed at 200° C. for 1 hour.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and was subjected to vacuum baking at 170° C. for 30 minutes in aheating chamber of the vacuum evaporation apparatus, and then thesubstrate 1100 was cooled down for about 30 minutes.

Next, the substrate 1100 was fixed to a holder provided in the vacuumevaporation apparatus so that a surface of the substrate 1100 over whichthe first electrode 1101 was formed faced downward. In this example, acase will be described in which the hole-injection layer 1111, thehole-transport layer 1112, the light-emitting layer 1113, theelectron-transport layer 1114, and the electron-injection layer 1115which are included in the EL layer 1102 are sequentially formed by avacuum evaporation method.

After reducing the pressure of the vacuum evaporation apparatus to 10⁻⁴Pa, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) andmolybdenum(VI) oxide were co-evaporated with a mass ratio of DBT3P-II(abbreviation) to molybdenum oxide being 4:2, whereby the hole-injectionlayer 1111 was formed over the first electrode 1101. The thickness ofthe hole-injection layer 1111 was 40 nm. Note that the co-evaporation isan evaporation method in which some different substances are evaporated,from some different evaporation sources at the same time.

Then, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:BPAFLP) was deposited by evaporation to a thickness of 20 nm, so thatthe hole-transport layer 1112 was formed.

Next, the light-emitting layer 1113 was formed over the hole-transportlayer 1112 in the following manner. Co-evaporated were2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II), 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBA1BP), and[2-(acetyl-κO)-cyclohexanonato-κO]bis[2-(3-methyl-4-pyrimidinyl-κN3)phenyl-κC]iridium(III)(abbreviation: [Ir(mppm)₂(achex)]) with a mass ratio of 2mDBTPDBq-II(abbreviation) to PCBA1BP (abbreviation) and [Ir(mppm)₂(achex)](abbreviation) being 0.8:0.2:0.025. The thickness of the light-emittinglayer 1113 was 40 nm.

Then, over the light-emitting layer 1113, 2mDBTPDBq-II (abbreviation)was deposited by evaporation to a thickness of 10 nm and thenbathophenanthroline (abbreviation: Bphen) was deposited by evaporationto a thickness of 20 nm, whereby the electron-transport layer 1114having a stacked structure was formed. Furthermore, lithium fluoride wasdeposited by evaporation to a thickness of 1 nm over theelectron-transport layer 1114, whereby the electron-injection layer 1115was formed.

Finally, aluminum was deposited by evaporation to a thickness of 200 nmover the electron-injection layer 1115 to form the second electrode 1103serving as a cathode; thus, the light-emitting element 2 was obtained.Note that in all the above evaporation steps, evaporation was performedby a resistance-heating method.

An element structure of the light-emitting element 2 obtained asdescribed above is shown in Table 3.

TABLE 3 Hole- Light- Electron- First Hole-injection transport emittingElectron- injection Second Electrode Layer Layer Layer transport LayerLayer Electrode Light- ITSO DBT3P-II:MoOx BPAFLP * ** Bphen LiF Alemitting (110 nm) (4:2 40 nm) (20 nm) (20 nm) (1 nm) (200 nm) Element2 * 2mDBTPDBq-II:PCBA1BP:[Ir(mppm)₂(achex)] (0.8:0.2:0.025 40 nm) **2mDBTPDBq-II (10 nm)

Further, the fabricated light-emitting element 2 was sealed in a glovebox containing a nitrogen atmosphere so as not to be exposed to the air.

Operation Characteristics of Light-Emitting Element 2

Operation characteristics of the fabricated light-emitting element 2were measured. Note that the measurement was carried out at roomtemperature (under an atmosphere in which the temperature was kept at25° C.).

FIG. 23 shows current density-luminance characteristics of thelight-emitting element 2. In FIG. 23, the vertical axis representsluminance (cd/m²) and the horizontal axis represents current density(mA/cm²). FIG. 24 shows voltage-luminance characteristics of thelight-emitting element 2. In FIG. 24, the vertical axis representsluminance (cd/m²) and the horizontal axis represents voltage (V).Further, FIG. 25 shows luminance-current efficiency characteristics ofthe light-emitting element 2. In FIG. 25, the vertical axis representscurrent efficiency (cd/A) and the horizontal axis represents luminance(cd/m²). FIG. 26 shows voltage-current characteristics of thelight-emitting element 2. In FIG. 26, the vertical axis representscurrent (mA) and the horizontal axis represents voltage (V).

FIG. 25 reveals high efficiency of the light-emitting element 2 in whichpart of the light-emitting layer uses [Ir(mppm)₂(achex)] (abbreviation),the phosphorescent organometallic iridium complex that is one embodimentof the present invention. Table 4 shows initial values of maincharacteristics of the light-emitting element at a luminance of about1000 cd/m².

TABLE 4 Current Current Power Quantum Voltage Current DensityChromaticity Luminance Efficiency Efficiency Efficiency (V) (mA)(mA/cm²) (x, y) (cd/m²) (cd/A) (lm/W) (%) Light- 2.9 0.043 1.1 (0.46,0.53) 820 77 84 22 emitting Element 2

The above results show that the light-emitting element 2 fabricated inthis example is a high-luminance light-emitting element having highcurrent efficiency. Moreover, as for color purity, it can be found thatthe light-emitting element exhibits yellow green light emission withexcellent color purity.

FIG. 27 shows an emission spectrum when a current at a current densityof 2.5 mA/cm² was supplied to the light-emitting element 2. As shown inFIG. 27, the emission spectrum of the light-emitting element 2 has apeak at around 560 nm and it is indicated that the peak is derived fromemission of the phosphorescent organometallic iridium complex[Ir(mppm)₂(achex)] (abbreviation).

Example 7

In this example, a light-emitting element 3 in which [Ir(mppm)₂(acpen)](abbreviation), the phosphorescent organometallic iridium complexrepresented by Structural Formula (104), is used for a light-emittinglayer is described. Note that in the description of the light-emittingelement 3 in this example, FIG. 17 which is used in the description ofthe light-emitting element 1 in Example 5 is to be referred to. Chemicalformulae of materials used in this example are shown below.

Fabrication of Light-Emitting Element 3

First, indium tin oxide containing silicon oxide (ITSO) was depositedover the glass substrate 1100 by a sputtering method, so that the firstelectrode 1101 which functions as an anode was formed. The thickness was110 nm and the electrode area was 2 mm×2 mm.

Then, as pretreatment for forming the light-emitting element over thesubstrate 1100, UV ozone treatment was performed for 370 seconds afterwashing of a surface of the substrate with water and baking that wasperformed at 200° C. for 1 hour.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and was subjected to vacuum baking at 170° C. for 30 minutes in aheating chamber of the vacuum evaporation apparatus, and then thesubstrate 1100 was cooled down for about 30 minutes.

Next, the substrate 1100 was fixed to a holder provided in the vacuumevaporation apparatus so that a surface of the substrate 1100 over whichthe first electrode 1101 was formed faced downward. In this example, acase will be described in which the hole-injection layer 1111, thehole-transport layer 1112, the light-emitting layer 1113, theelectron-transport layer 1114, and the electron-injection layer 1115which are included in the EL layer 1102 are sequentially formed by avacuum evaporation method.

After reducing the pressure of the vacuum evaporation apparatus to 10⁻⁴Pa, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) andmolybdenum(VI) oxide were co-evaporated with a mass ratio of DBT3P-II(abbreviation) to molybdenum oxide being 4:2, whereby the hole-injectionlayer 1111 was formed over the first electrode 1101. The thickness ofthe hole-injection layer 1111 was 40 nm. Note that the co-evaporation isan evaporation method in which some different substances are evaporatedfrom some different evaporation sources at the same time.

Then, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:BPAFLP) was deposited by evaporation to a thickness of 20 nm, so thatthe hole-transport layer 1112 was formed.

Next, the light-emitting layer 1113 was formed over the hole-transportlayer 1112 in the following manner. Co-evaporated were2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II), 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBA1BP), and[2-(acetyl-κO)-cyclopentanonato-κO]bis[2-(6-methyl-4-pyrimidinyl-κN3)phenyl-κC]iridium(III)(abbreviation: [Ir(mppm)₂(acpen)]) with a mass ratio of 2mDBTPDBq-II(abbreviation) to PCBA1BP (abbreviation) and [Ir(mppm)₂(acpen)](abbreviation) being 0.8:0.2:0.025. The thickness of the light-emittinglayer 1113 was 40 nm.

Then, over the light-emitting layer 1113, 2mDBTPDBq-II (abbreviation)was deposited by evaporation to a thickness of 10 nm and thenbathophenanthroline (abbreviation: Bphen) was deposited by evaporationto a thickness of 20 nm, whereby the electron-transport layer 1114having a stacked structure was formed. Furthermore, lithium fluoride wasdeposited by evaporation to a thickness of 1 nm over theelectron-transport layer 1114, whereby the electron-injection layer 1115was formed.

Finally, aluminum was deposited by evaporation to a thickness of 200 nmover the electron-injection layer 1115 to form the second electrode 1103serving as a cathode; thus, the light-emitting element 3 was obtained.Note that in all the above evaporation steps, evaporation was performedby a resistance-heating method.

An element structure of the light-emitting element 3 obtained asdescribed above is shown in Table 5.

TABLE 5 Hole- Light- Electron- First Hole-injection transport emittingElectron- injection Second Electrode Layer Layer Layer transport LayerLayer Electrode Light- ITSO DBT3P-II:MoOx BPAFLP * ** Bphen LiF Alemitting (110 nm) (4:2 40 nm) (20 nm) (20 nm) (1 nm) (200 nm) Element3 * 2mDBTPDBq-II:PCBA1BP:[Ir(mppm)₂(acpen)] (0.8:0.2:0.025 40 nm) **2mDBTPDBq-II (10 nm)

Further, the fabricated light-emitting element 3 was sealed in a glovebox containing a nitrogen atmosphere so as not to be exposed to the air.

Operation Characteristics of Light-Emitting Element 3

Operation characteristics of the fabricated light-emitting element 3were measured. Note that the measurement was carried out at roomtemperature (under an atmosphere in which the temperature was kept at25° C.).

FIG. 28 shows current density-luminance characteristics of thelight-emitting element 3. In FIG. 28, the vertical axis representsluminance (cd/m²) and the horizontal axis represents current density(mA/cm²). FIG. 29 shows voltage-luminance characteristics of thelight-emitting element 3. In FIG. 29, the vertical axis representsluminance (cd/m²) and the horizontal axis represents voltage (V).Further, FIG. 30 shows luminance-current efficiency characteristics ofthe light-emitting element 3. In FIG. 30, the vertical axis representscurrent efficiency (cd/A) and the horizontal axis represents luminance(cd/m²). FIG. 31 shows voltage-current characteristics of thelight-emitting element 3. In FIG. 31, the vertical axis representscurrent (mA) and the horizontal, axis represents voltage (V).

FIG. 30 reveals high efficiency of the light-emitting element 3 in whichpart of the light-emitting layer uses [Ir(mppm)₂(acpen)] (abbreviation),the phosphorescent organometallic iridium complex that is one embodimentof the present invention. Table 6 shows initial values of maincharacteristics of the light-emitting element at a luminance of about1000 cd/m².

TABLE 6 Current Current Power Quantum Voltage Current DensityChromaticity Luminance Efficiency Efficiency Efficiency (V) (mA)(mA/cm²) (x, y) (cd/m²) (cd/A) (lm/W) (%) Light- 2.9 0.049 1.2 (0.43,0.56) 1000 83 90 23 emitting Element 3

The above results show that the light-emitting element 3 fabricated inthis example is a high-luminance light-emitting element having highcurrent efficiency. Moreover, as for color purity, it can be found thatthe light-emitting element exhibits yellow green light emission withexcellent color purity.

FIG. 32 shows an emission spectrum when a current at a current densityof 2.5 mA/cm² was supplied to the light-emitting element 3. As shown inFIG. 32, the emission spectrum of the light-emitting element 3 has apeak at around 550 nm and it is indicated that the peak is derived fromemission of the phosphorescent organometallic iridium complex[Ir(mppm)₂(acpen)] (abbreviation).

This application is based on Japanese Patent Application serial no.2011-261289 filed with Japan Patent Office on Nov. 30, 2011, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. An organometallic complex having a structurerepresented by General Formula (G1),

wherein: L represents a bidentate aromatic ligand and has at least abond between carbon of an aromatic ring in the aromatic ligand and Ir, Xrepresents a five-membered or six-membered alicycle composed of carbonand hydrogen, and R¹ represents a substituted or unsubstituted alkylgroup having 1 to 4 carbon atoms.
 2. The organometallic complexaccording to claim 1, wherein the aromatic ligand is anitrogen-containing heteroaromatic ring derivative substituted by anaryl group or a nitrogen-containing heterocyclic carbene derivativesubstituted by an aryl group, and wherein a site of substitution of thearyl group is a carbon atom adjacent to a nitrogen atom of thenitrogen-containing heteroaromatic ring or a nitrogen atom adjacent to acarbene carbon atom.
 3. The organometallic complex according to claim 1,wherein the aromatic ligand is represented by any one of GeneralFormulae (L1) to (L3),

wherein: R⁶ to R⁹ separately represent hydrogen, a substituted orunsubstituted alkyl group having 1 to 4 carbon atoms, or a substitutedor unsubstituted phenyl group, and A² to A⁶ separately represent oxygen,sulfur, nitrogen, sp² hybridized nitrogen bonded to any of an alkylgroup having 1 to 4 carbon atoms and a phenyl group, sp² hybridizedcarbon bonded to hydrogen, or sp² hybridized carbon bonded to any of analkyl group having 1 to 4 carbon atoms and a phenyl group.
 4. Theorganometallic complex according to claim 1, wherein the organometalliccomplex is represented by General Formula (G2) or (G3),

wherein: X represents a five-membered or six-membered alicycle composedof carbon and hydrogen, R¹ represents a substituted or unsubstitutedalkyl group having 1 to 4 carbon atoms, and R² to R⁹ separatelyrepresent a substituted or unsubstituted alkyl group having 1 to 4carbon atoms, or a substituted or unsubstituted phenyl group.
 5. Theorganometallic complex according to claim 1, wherein the organometalliccomplex is represented by Structural Formula (100) or (104),


6. A light-emitting element comprising the organometallic complexaccording to claim
 1. 7. A light-emitting device comprising thelight-emitting element according to claim
 6. 8. An electronic devicecomprising the light-emitting device according to claim
 7. 9. A lightingdevice comprising the light-emitting device according to claim
 7. 10. Anorganometallic complex represented by Structural Formula (101),


11. A light-emitting element comprising the organometallic complexaccording to claim
 10. 12. A light-emitting device comprising thelight-emitting element according to claim
 11. 13. An electronic devicecomprising the light-emitting device according to claim
 12. 14. Alighting device comprising the light-emitting device according to claim12.
 15. An organometallic complex represented by Structural Formula(113),


16. A light-emitting element comprising the organometallic complexaccording to claim
 15. 17. A light-emitting device comprising thelight-emitting element according to claim
 16. 18. An electronic devicecomprising the light-emitting device according to claim
 17. 19. Alighting device comprising the light-emitting device according to claim17.